Merge 33dae6dc891b26d53381623dd5906082e7dda0f6 into d38ec3fe06b95a6bf1abe7ac4aa3fd8622d1c375

notes/算法.md

@@ -421,6 +421,56 @@ public class Shell<T extends Comparable<T>> extends Sort<T> {
 
 ### 1. 归并方法
 
+package sortdemo;
+
+import java.util.Arrays;
+
+/**
+ * Created by chengxiao on 2016/12/8.
+ */
+public class MergeSort {
+    public static void main(String []args){
+        int []arr = {9,8,7,6,5,4,3,2,1};
+        sort(arr);
+        System.out.println(Arrays.toString(arr));
+    }
+    public static void sort(int []arr){
+        int []temp = new int[arr.length];//在排序前，先建好一个长度等于原数组长度的临时数组，避免递归中频繁开辟空间
+        sort(arr,0,arr.length-1,temp);
+    }
+    private static void sort(int[] arr,int left,int right,int []temp){
+        if(left<right){
+            int mid = (left+right)/2;
+            sort(arr,left,mid,temp);//左边归并排序，使得左子序列有序
+            sort(arr,mid+1,right,temp);//右边归并排序，使得右子序列有序
+            merge(arr,left,mid,right,temp);//将两个有序子数组合并操作
+        }
+    }
+    private static void merge(int[] arr,int left,int mid,int right,int[] temp){
+        int i = left;//左序列指针
+        int j = mid+1;//右序列指针
+        int t = 0;//临时数组指针
+        while (i<=mid && j<=right){
+            if(arr[i]<=arr[j]){
+                temp[t++] = arr[i++];
+            }else {
+                temp[t++] = arr[j++];
+            }
+        }
+        while(i<=mid){//将左边剩余元素填充进temp中
+            temp[t++] = arr[i++];
+        }
+        while(j<=right){//将右序列剩余元素填充进temp中
+            temp[t++] = arr[j++];
+        }
+        t = 0;
+        //将temp中的元素全部拷贝到原数组中
+        while(left <= right){
+            arr[left++] = temp[t++];
+        }
+    }
+}
+
 归并方法将数组中两个已经排序的部分归并成一个。
 
 ```java