diff --git a/code/src/main/java/com/raorao/leetcode/q017/PhoneNumber.java b/code/src/main/java/com/raorao/leetcode/q017/PhoneNumber.java new file mode 100644 index 00000000..538d82c2 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q017/PhoneNumber.java @@ -0,0 +1,45 @@ +package com.raorao.leetcode.q017; + +import java.util.ArrayList; +import java.util.List; + +/** + * 电话键盘组合. + * + * @author Xiong Raorao + * @since 2018-08-22-18:46 + */ +public class PhoneNumber { + + private final static String[] KEYS = new String[] {"", "", "abc", "def", "ghi", "jkl", "mno", + "pqrs", "tuv", "wxyz"}; + + public static void main(String[] args) { + List ret = new PhoneNumber().letterCombinations("23"); + System.out.println(ret); + + } + + public List letterCombinations(String digits) { + List ret = new ArrayList<>(); + int[] index = new int[digits.length()]; + for (int i = 0; i < index.length; i++) { + index[i] = digits.charAt(i) - '0'; + } + process(new StringBuilder(), ret, index); + return ret; + } + + private void process(StringBuilder prefix, List ret, int[] index) { + if (prefix.length() == index.length) { + ret.add(prefix.toString()); + return; + } + for (char c : KEYS[index[prefix.length()]].toCharArray()) { + prefix.append(c); + process(prefix, ret, index); + prefix.deleteCharAt(prefix.length() - 1); + } + } + +} diff --git a/code/src/main/java/com/raorao/leetcode/q037/Shudu.java b/code/src/main/java/com/raorao/leetcode/q037/Shudu.java new file mode 100644 index 00000000..3e634005 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q037/Shudu.java @@ -0,0 +1,70 @@ +package com.raorao.leetcode.q037; + +/** + * 数独问题. + * + * @author Xiong Raorao + * @since 2018-08-23-9:30 + */ +public class Shudu { + + private boolean[][] rowsUsed = new boolean[9][10]; + private boolean[][] colsUsed = new boolean[9][10]; + private boolean[][] cubesUsed = new boolean[9][10]; + private char[][] board; + + public static void main(String[] args) { + + } + + public void solveSudoku(char[][] board) { + this.board = board; + for (int i = 0; i < 9; i++) { + for (int j = 0; j < 9; j++) { + if (board[i][j] == '.') { + continue; + } + int num = board[i][j] - '0'; + rowsUsed[i][num] = true; + colsUsed[j][num] = true; + cubesUsed[cubeNum(i, j)][num] = true; + } + } + + for (int i = 0; i < 9; i++) { + for (int j = 0; j < 9; j++) { + backtracking(i, j); + } + } + } + + private boolean backtracking(int row, int col) { + while (row < 9 && board[row][col] != '.') { + row = col == 8 ? row + 1 : row; + col = col == 8 ? 0 : col + 1; + } + if (row == 9) { + return true; + } + for (int num = 1; num <= 9; num++) { + if (rowsUsed[row][num] || colsUsed[col][num] || cubesUsed[cubeNum(row, col)][num]) { + continue; + } + rowsUsed[row][num] = colsUsed[col][num] = cubesUsed[cubeNum(row, col)][num] = true; + board[row][col] = (char) (num + '0'); + if (backtracking(row, col)) { + return true; + } + board[row][col] = '.'; + rowsUsed[row][num] = colsUsed[col][num] = cubesUsed[cubeNum(row, col)][num] = false; + } + return false; + } + + private int cubeNum(int i, int j) { + int r = i / 3; + int c = j / 3; + return r * 3 + c; + } + +} diff --git a/code/src/main/java/com/raorao/leetcode/q046/Permutation.java b/code/src/main/java/com/raorao/leetcode/q046/Permutation.java new file mode 100644 index 00000000..2623bbf9 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q046/Permutation.java @@ -0,0 +1,43 @@ +package com.raorao.leetcode.q046; + +import java.util.ArrayList; +import java.util.List; + +/** + * 排列. + * + * @author Xiong Raorao + * @since 2018-08-23-8:58 + */ +public class Permutation { + + public static void main(String[] args) { + int[] input = new int[] {1, 2, 3}; + new Permutation().permute(input); + } + + public List> permute(int[] nums) { + List> permutes = new ArrayList<>(); + boolean[] visited = new boolean[nums.length]; + back(nums, new ArrayList<>(), permutes, visited); + return permutes; + } + + private void back(int[] arr, List level, List> lists, + boolean[] visited) { + if (level.size() == arr.length) { + lists.add(new ArrayList<>(level)); + return; + } + for (int i = 0; i < arr.length; i++) { + if(visited[i]){ + continue; + } + visited[i] = true; + level.add(arr[i]); + back( arr, level, lists, visited); + level.remove(level.size() - 1); + visited[i] = false; + } + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q064/MinPathSum.java b/code/src/main/java/com/raorao/leetcode/q064/MinPathSum.java new file mode 100644 index 00000000..98e11b27 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q064/MinPathSum.java @@ -0,0 +1,41 @@ +package com.raorao.leetcode.q064; + +import java.util.Arrays; + +/** + * 矩阵最小路径和. + * + * @author Xiong Raorao + * @since 2018-08-23-10:56 + */ +public class MinPathSum { + + public static void main(String[] args) { + int[][] grid = new int[][] { + {1, 3, 1}, + {1, 5, 1}, + {4, 2, 1}}; + int res = new MinPathSum().minPathSum(grid); + System.out.println(res); + } + + public int minPathSum(int[][] grid) { + if (grid == null) { + return 0; + } + int rowLen = grid.length; + int colLen = grid[0].length; + int[] res = new int[colLen + 1]; + Arrays.fill(res, Integer.MAX_VALUE); + res[1] = 0; + for (int i = 1; i <= rowLen; i++) { + for (int j = 1; j <= colLen; j++) { + //当前点的最小路径和为 : 从左边和上边选择最小的路径和再加上当前点的值 + //res[j]没更新之前就表示i-1行到第j个元素的最小路径和 + //因为是从左往右更新,res[j-1]表示i行第j-1个元素的最小路径和 + res[j] = Math.min(res[j], res[j - 1]) + grid[i - 1][j - 1]; + } + } + return res[colLen]; + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q079/WordSearch.java b/code/src/main/java/com/raorao/leetcode/q079/WordSearch.java new file mode 100644 index 00000000..f6db5940 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q079/WordSearch.java @@ -0,0 +1,62 @@ +package com.raorao.leetcode.q079; + +/** + * 在矩阵中寻找字符串. + * + * @author Xiong Raorao + * @since 2018-08-23-7:44 + */ +public class WordSearch { + + private static final int[][] direction = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}}; + private static int m; + private static int n; + + public static void main(String[] args) { + char[][] input = new char[][] { + {'A', 'B', 'C', 'E'}, + {'S', 'F', 'C', 'S'}, + {'A', 'D', 'E', 'E'}, + }; + String word = "ABCCED"; + System.out.println(new WordSearch().exist(input, word)); + } + + public boolean exist(char[][] board, String word) { + if (board == null || board.length == 0) { + return false; + } + m = board.length; + n = board[0].length; + boolean[][] hasVisited = new boolean[m][n]; + for (int i = 0; i < m; i++) { + for (int j = 0; j < n; j++) { + if (back(board, 0, i, j, hasVisited, word)) { + return true; + } + } + } + return false; + } + + private boolean back(char[][] board, int current, int i, int j, boolean[][] hasVisited, + String word) { + if (current == word.length()) { + return true; + } + if (i < 0 || i >= m || j < 0 || j >= n || board[i][j] != word.charAt(current) + || hasVisited[i][j]) { + return false; + } + hasVisited[i][j] = true; + for (int[] d : direction) { + if (back(board, current + 1, i + d[0], j + d[1], hasVisited, word)) { + return true; + } + } + hasVisited[i][j] = false; + return false; + } + + +} diff --git a/code/src/main/java/com/raorao/leetcode/q093/RestoreIP.java b/code/src/main/java/com/raorao/leetcode/q093/RestoreIP.java new file mode 100644 index 00000000..59c6f8d4 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q093/RestoreIP.java @@ -0,0 +1,54 @@ +package com.raorao.leetcode.q093; + +import java.util.ArrayList; +import java.util.List; + +/** + * ip地址的划分. + * + * @author Xiong Raorao + * @since 2018-08-22-20:38 + */ +public class RestoreIP { + + public static void main(String[] args) { + String input = "25525511135"; + List ret = new RestoreIP().restoreIpAddresses(input); + ret.forEach(e -> System.out.print(e + " ")); + } + + public List restoreIpAddresses(String s) { + List ret = new ArrayList<>(); + process(0, new StringBuilder(), ret, s); + return ret; + } + + /** + * @param k 表示当前已经分割的ip段 + */ + private void process(int k, StringBuilder sb, List ret, String s) { + + if (k == 4 || s.length() == 0) { + if (k == 4 && s.length() == 0) { + ret.add(sb.toString()); + } + return; + } + + for (int i = 0; i < s.length() && i <= 2; i++) { + if (i != 0 && s.charAt(0) == '0') { + break; + } + String part = s.substring(0, i + 1); + if (Integer.valueOf(part) <= 255) { + if (sb.length() != 0) { + part = "." + part; + } + sb.append(part); + process(k + 1, sb, ret, s.substring(i + 1)); + sb.delete(sb.length() - part.length(), sb.length()); + } + } + + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q102/LevelOrder.java b/code/src/main/java/com/raorao/leetcode/q102/LevelOrder.java new file mode 100644 index 00000000..f306181c --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q102/LevelOrder.java @@ -0,0 +1,91 @@ +package com.raorao.leetcode.q102; + +import java.util.ArrayList; +import java.util.LinkedList; +import java.util.List; +import java.util.Queue; +import java.util.Stack; + +/** + * 二叉树的层次遍历. + * + * @author Xiong Raorao + * @since 2018-08-22-10:43 + */ +public class LevelOrder { + + public static void main(String[] args) { + + } + + public List> levelOrder(TreeNode root) { + List> ret = new ArrayList<>(); + if (root == null) { + return ret; + } + Queue queue = new LinkedList<>(); + queue.add(root); + while (!queue.isEmpty()) { + int levelSize = queue.size(); + List levelList = new ArrayList<>(); + while (levelSize-- > 0) { + TreeNode node = queue.poll(); + if (node != null) { + levelList.add(node.val); + if (node.left != null) { + queue.add(node.left); + } + if (node.right != null) { + queue.add(node.right); + } + } + } + ret.add(levelList); + } + return ret; + } + + public List> levelOrderBottom(TreeNode root) { + List> ret = new ArrayList<>(); + if (root == null) { + return ret; + } + Queue queue = new LinkedList<>(); + queue.add(root); + Stack> listStack = new Stack<>(); + while (!queue.isEmpty()) { + int levelSize = queue.size(); + List levelList = new ArrayList<>(); + while (levelSize-- > 0) { + TreeNode node = queue.poll(); + if (node != null) { + levelList.add(node.val); + if (node.left != null) { + queue.add(node.left); + } + if (node.right != null) { + queue.add(node.right); + } + } + } + listStack.add(levelList); + } + while (!listStack.isEmpty()) { + ret.add(listStack.pop()); + } + return ret; + } + + + static class TreeNode { + + int val; + TreeNode left; + TreeNode right; + + TreeNode(int x) { + val = x; + } + } + +} diff --git a/code/src/main/java/com/raorao/leetcode/q111/BTreeDepth.java b/code/src/main/java/com/raorao/leetcode/q111/BTreeDepth.java new file mode 100644 index 00000000..c68fd0e9 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q111/BTreeDepth.java @@ -0,0 +1,57 @@ +package com.raorao.leetcode.q111; + + +import java.util.LinkedList; +import java.util.Queue; + +/** + * 求二叉树的最小深度. + * + * @author Xiong Raorao + * @since 2018-08-22-14:33 + */ +public class BTreeDepth { + + public static void main(String[] args) { + + } + + public int minDepth(TreeNode root) { + Queue queue = new LinkedList<>(); + if (root == null) { + return 0; + } + queue.add(root); + int level = 1; + while (!queue.isEmpty()) { + int levelSize = queue.size(); + while (levelSize-- > 0) { + TreeNode node = queue.poll(); + if (node != null) { + if (node.left != null) { + queue.add(node.left); + } + if (node.right != null) { + queue.add(node.right); + } + if (node.left == null && node.right == null) { + return level; + } + } + } + level++; + } + return level; + } + + public class TreeNode { + + int val; + TreeNode left; + TreeNode right; + + TreeNode(int x) { + val = x; + } + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q127/WordLadder.java b/code/src/main/java/com/raorao/leetcode/q127/WordLadder.java new file mode 100644 index 00000000..631948d7 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q127/WordLadder.java @@ -0,0 +1,95 @@ +package com.raorao.leetcode.q127; + +import java.util.ArrayList; +import java.util.Arrays; +import java.util.LinkedList; +import java.util.List; +import java.util.Queue; + +/** + * 单词接龙. + * + * @author Xiong Raorao + * @since 2018-08-22-10:02 + */ +public class WordLadder { + + public static void main(String[] args) { + String beginWord = "hit"; + String endWord = "cog"; + //List wordList = Arrays.asList("hot", "dot", "dog", "lot", "log", "cog"); + List wordList = new ArrayList<>(); + wordList.add("hot"); + wordList.add("dot"); + wordList.add("lot"); + wordList.add("log"); + wordList.add("cog"); + int result = new WordLadder().ladderLength(beginWord, endWord, wordList); + System.out.println(result); + } + + public int ladderLength(String beginWord, String endWord, List wordList) { + wordList.add(beginWord); + int N = wordList.size(); + int start = N - 1; + int end = 0; + while (end < N && !wordList.get(end).equals(endWord)) { + end++; + } + if (end == N) { + return 0; + } + List[] graphic = buildGraphic(wordList); + return getShortestPath(graphic, start, end); + } + + private List[] buildGraphic(List wordList) { + int N = wordList.size(); + List[] graphic = new List[N]; + for (int i = 0; i < N; i++) { + graphic[i] = new ArrayList<>(); + for (int j = 0; j < N; j++) { + if (isConnect(wordList.get(i), wordList.get(j))) { + graphic[i].add(j); + } + } + } + return graphic; + } + + private boolean isConnect(String s1, String s2) { + int diffCnt = 0; + for (int i = 0; i < s1.length() && diffCnt <= 1; i++) { + if (s1.charAt(i) != s2.charAt(i)) { + diffCnt++; + } + } + return diffCnt == 1; + } + + private int getShortestPath(List[] graphic, int start, int end) { + Queue queue = new LinkedList<>(); + boolean[] marked = new boolean[graphic.length]; + queue.add(start); + marked[start] = true; + int path = 1; + while (!queue.isEmpty()) { + int size = queue.size(); + path++; + while (size-- > 0) { + int cur = queue.poll(); + for (int next : graphic[cur]) { + if (next == end) { + return path; + } + if (marked[next]) { + continue; + } + marked[next] = true; + queue.add(next); + } + } + } + return 0; + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q130/SurroundedRegion.java b/code/src/main/java/com/raorao/leetcode/q130/SurroundedRegion.java new file mode 100644 index 00000000..468bbc9f --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q130/SurroundedRegion.java @@ -0,0 +1,82 @@ +package com.raorao.leetcode.q130; + +import java.util.LinkedList; +import java.util.Queue; + +/** + * 被围绕的区域. + * + * @author Xiong Raorao + * @since 2018-08-22-14:53 + */ +public class SurroundedRegion { + + private static Queue queue = null; + private static int rows = 0; + private static int cols = 0; + + public static void main(String[] args) { + char[][] board = new char[][] { + {'X', 'X', 'X', 'X'}, + {'X', 'O', 'O', 'X'}, + {'X', 'X', 'O', 'X'}, + {'X', 'O', 'X', 'X'}}; + new SurroundedRegion().solve(board); + } + + public void solve(char[][] board) { + if (board.length == 0 || board[0].length == 0) { + return; + } + queue = new LinkedList(); + rows = board.length; + cols = board[0].length; + + for (int i = 0; i < rows; i++) { // **important** + enqueue(i, 0, board); + enqueue(i, cols - 1, board); + } + + for (int j = 1; j < cols - 1; j++) { // **important** + enqueue(0, j, board); + enqueue(rows - 1, j, board); + } + + // 把所有边界为O的元素的位置以及和边界连通的’O‘放到队列中去，已经放入队列的改为'D' + while (!queue.isEmpty()) { + int cur = queue.poll(); + int x = cur / cols, + y = cur % cols; + + if (board[x][y] == 'O') { + board[x][y] = 'D'; + } + + enqueue(x - 1, y, board); + enqueue(x + 1, y, board); + enqueue(x, y - 1, board); + enqueue(x, y + 1, board); + } + + for (int i = 0; i < rows; i++) { + for (int j = 0; j < cols; j++) { + if (board[i][j] == 'D') { + board[i][j] = 'O'; + } else if (board[i][j] == 'O') { + board[i][j] = 'X'; + } + } + } + + queue = null; + board = null; + rows = 0; + cols = 0; + } + + public void enqueue(int x, int y, char[][] board) { + if (x >= 0 && x < rows && y >= 0 && y < cols && board[x][y] == 'O') { + queue.offer(x * cols + y); + } + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q198/Robber.java b/code/src/main/java/com/raorao/leetcode/q198/Robber.java new file mode 100644 index 00000000..45782f23 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q198/Robber.java @@ -0,0 +1,33 @@ +package com.raorao.leetcode.q198; + +/** + * 强盗抢劫. + * + * @author Xiong Raorao + * @since 2018-08-23-10:09 + */ +public class Robber { + + public static void main(String[] args) { + int[] input = new int[] {1, 2, 3, 1}; + int result = new Robber().rob(input); + System.out.println(result); + } + + public int rob(int[] nums) { + if (nums == null || nums.length == 0) { + return 0; + } + int n = nums.length; + int pre1 = 0; + int pre2 = 0; + int pre3 = 0; + for (int i = 0; i < n; i++) { + int cur = Math.max(pre2, pre3) + nums[i]; + pre3 = pre2; + pre2 = pre1; + pre1 = cur; + } + return Math.max(pre1, pre2); + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q200/NumIslands.java b/code/src/main/java/com/raorao/leetcode/q200/NumIslands.java new file mode 100644 index 00000000..6167f30d --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q200/NumIslands.java @@ -0,0 +1,50 @@ +package com.raorao.leetcode.q200; + +/** + * 求岛屿的个数. + * + * @author Xiong Raorao + * @since 2018-08-22-16:53 + */ +public class NumIslands { + + private final int[][] directions = new int[][] {{1, 0}, {-1, 0}, {0, 1}, {0, -1}}; + + public static void main(String[] args) { + char[][] grid = new char[][] { + {'1', '1', '1', '1', '0'}, + {'1', '1', '0', '1', '0'}, + {'1', '1', '0', '0', '0'}, + {'0', '0', '0', '0', '0'}}; + int result = new NumIslands().numIslands(grid); + System.out.println(result); + } + + public int numIslands(char[][] grid) { + if (grid == null || grid.length == 0) { + return 0; + } + int m = grid.length; + int n = grid[0].length; + int islandNum = 0; + for (int i = 0; i < m; i++) { + for (int j = 0; j < n; j++) { + if (grid[i][j] == '1') { + dfs(grid, i, j); + islandNum++; + } + } + } + return islandNum; + } + + private void dfs(char[][] grid, int i, int j) { + if (i < 0 || i >= grid.length || j < 0 || j >= grid[0].length || grid[i][j] == '0') { + return; + } + grid[i][j] = '0'; + for (int[] d : directions) { + dfs(grid, i + d[0], j + d[1]); + } + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q257/BinaryTreePath.java b/code/src/main/java/com/raorao/leetcode/q257/BinaryTreePath.java new file mode 100644 index 00000000..ee10c980 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q257/BinaryTreePath.java @@ -0,0 +1,66 @@ +package com.raorao.leetcode.q257; + +import java.util.ArrayList; +import java.util.List; + +/** + * 输出二叉树的叶子节点的路径. + * + * @author Xiong Raorao + * @since 2018-08-23-8:24 + */ +public class BinaryTreePath { + + public static void main(String[] args) { + TreeNode root = new TreeNode(1); + TreeNode left = new TreeNode(2); + left.right = new TreeNode(5); + TreeNode right = new TreeNode(3); + root.left = left; + root.right = right; + List str = new BinaryTreePath().binaryTreePaths(root); + str.forEach(System.out::println); + } + + public List binaryTreePaths(TreeNode root) { + List path = new ArrayList<>(); + if (root == null) { + return path; + } + List values = new ArrayList<>(); + back(values, root, path); + return path; + } + + private void back(List values, TreeNode root, List path) { + if (root == null) { + return; + } + values.add(root); + if (root.left == null && root.right == null) { + path.add(build(values)); + } + back(values, root.left, path); + back(values, root.right, path); + values.remove(root); + } + + private String build(List node) { + StringBuilder sb = new StringBuilder(); + node.forEach(e -> sb.append(e.val).append("->")); + String tmp = sb.toString(); + return tmp.substring(0, tmp.length() - 2); + } + + static class TreeNode { + + int val; + TreeNode left; + TreeNode right; + + TreeNode(int x) { + val = x; + } + } + +} diff --git a/code/src/main/java/com/raorao/leetcode/q279/PerfectSquare.java b/code/src/main/java/com/raorao/leetcode/q279/PerfectSquare.java new file mode 100644 index 00000000..dff1958b --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q279/PerfectSquare.java @@ -0,0 +1,27 @@ +package com.raorao.leetcode.q279; + +import java.util.ArrayList; +import java.util.List; + +/** + * 完全平方数. + * + * 题目描述：给定正整数 n，找到若干个完全平方数（比如 1, 4, 9, 16, ...）使得它们的和等于 n。你需要让组成和的完全平方数的个数最少。 + * + * @author Xiong Raorao + * @since 2018-08-22-9:29 + */ +public class PerfectSquare { + + public static void main(String[] args) { + + } + + private static List generate(int n) { + List ret = new ArrayList<>(); + for (int i = 1; i * i < n; i++) { + ret.add(i * i); + } + return ret; + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q547/FriendCycle.java b/code/src/main/java/com/raorao/leetcode/q547/FriendCycle.java new file mode 100644 index 00000000..1fed062d --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q547/FriendCycle.java @@ -0,0 +1,44 @@ +package com.raorao.leetcode.q547; + +/** + * 朋友圈. + * + * @author Xiong Raorao + * @since 2018-08-22-17:08 + */ +public class FriendCycle { + + public static void main(String[] args) { + int[][] M = new int[][] { + {1, 1, 0}, + {1, 1, 0}, + {0, 0, 1}}; + int result = new FriendCycle().findCircleNum(M); + System.out.println(result); + } + + public int findCircleNum(int[][] M) { + if (M == null || M.length == 0) { + return 0; + } + int n = M.length;// 朋友圈人数 + int num = 0; + boolean[] hasVisited = new boolean[n]; + for (int i = 0; i < n; i++) { + if (!hasVisited[i]) { + dfs(M, hasVisited, i); + num++; + } + } + return num; + } + + private void dfs(int[][] M, boolean[] hasVisited, int i) { + hasVisited[i] = true; + for (int k = 0; k < M.length; k++) { + if (M[i][k] == 1 && !hasVisited[k]) { + dfs(M, hasVisited, k); + } + } + } +} diff --git a/code/src/main/java/com/raorao/leetcode/q695/MaxArea.java b/code/src/main/java/com/raorao/leetcode/q695/MaxArea.java new file mode 100644 index 00000000..2cff70f9 --- /dev/null +++ b/code/src/main/java/com/raorao/leetcode/q695/MaxArea.java @@ -0,0 +1,55 @@ +package com.raorao.leetcode.q695; + +/** + * 岛屿的最大面积. + * + * @author Xiong Raorao + * @since 2018-08-22-16:06 + */ +public class MaxArea { + + private final int[][] directions = new int[][] {{1, 0}, {-1, 0}, {0, 1}, {0, -1}}; + + public static void main(String[] args) { + int[][] grid = new int[][] { + {0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0}, + {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0}, + {0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0}, + {0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0}, + {0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0}, + {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0}, + {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0}, + {0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0}}; + + int result = new MaxArea().maxAreaOfIsland(grid); + System.out.println(result); + } + + public int maxAreaOfIsland(int[][] grid) { + int maxArea = 0; + if (grid == null || grid.length == 0) { + return 0; + } + int row = grid.length; + int col = grid[0].length; + for (int i = 0; i < row; i++) { + for (int j = 0; j < col; j++) { + maxArea = Math.max(maxArea, dfs(grid, i, j)); + } + } + return maxArea; + + } + + private int dfs(int[][] grid, int m, int n) { + if (m < 0 || m >= grid.length || n < 0 || n >= grid[0].length || grid[m][n] == 0) { + return 0; + } + int area = 1; + grid[m][n] = 0; // 统计过了就置零 + for (int[] d : directions) { + area += dfs(grid, m + d[0], n + d[1]); + } + return area; + } +} diff --git a/interview/note.md b/interview/note.md index 36247f49..11482a43 100644 --- a/interview/note.md +++ b/interview/note.md @@ -39,6 +39,8 @@ Java后端开发（大数据、分布式应用等） 京东 | 8.4 | 8.20 |
  • 简历截止：8.30
  • 笔试时间 9.9
  • 面试时间 9.16-9.20
    • 微众银行| 8.20 | 8.20 | 华为 |8.1 | 8.21 +百度 | 8.22 | 8.22(新投递) | +网易 | 8.22 | 8.22(新投递) | # 2 复习内容 diff --git a/notes/Leetcode 题解.md b/notes/Leetcode 题解.md index 68af3cb7..a6345741 100644 --- a/notes/Leetcode 题解.md +++ b/notes/Leetcode 题解.md @@ -2505,24 +2505,23 @@ Given the above grid map, return 7. Because the path 1→3→1→1→1 minimizes 题目描述：求从矩阵的左上角到右下角的最小路径和，每次只能向右和向下移动。 ```java -public int minPathSum(int[][] grid) { - if (grid.length == 0 || grid[0].length == 0) { - return 0; + if (grid == null) { + return 0; } - int m = grid.length, n = grid[0].length; - int[] dp = new int[n]; - for (int i = 0; i < m; i++) { - for (int j = 0; j < n; j++) { - if (i == 0) { - dp[j] = dp[j - 1]; - } else { - dp[j] = Math.min(dp[j - 1], dp[j]); - } - dp[j] += grid[i][j]; - } + int rowLen = grid.length; + int colLen = grid[0].length; + int[] res = new int[colLen + 1]; + Arrays.fill(res, Integer.MAX_VALUE); + res[1] = 0; + for (int i = 1; i <= rowLen; i++) { + for (int j = 1; j <= colLen; j++) { + //当前点的最小路径和为 : 从左边和上边选择最小的路径和再加上当前点的值 + //res[j]没更新之前就表示i-1行到第j个元素的最小路径和 + //因为是从左往右更新,res[j-1]表示i行第j-1个元素的最小路径和 + res[j] = Math.min(res[j], res[j - 1]) + grid[i - 1][j - 1]; + } } - return dp[n - 1]; -} + return res[colLen]; ``` **矩阵的总路径数**