Update Leetcode 题解 - 排序.md

update quicksort

notes/Leetcode 题解 - 排序.md

@@ -17,6 +17,38 @@
 用于求解   **Kth Element**   问题，也就是第 K 个元素的问题。
 
 可以使用快速排序的 partition() 进行实现。需要先打乱数组，否则最坏情况下时间复杂度为 O(N<sup>2</sup>)。
+```java
+class Solution {
+    public int findKthLargest(int[] nums, int k) {
+        int left = 0, right = nums.length - 1;
+        int targetIndex = nums.length - k;
+        while (left < right) {
+            int index = partition(nums, left, right);
+            if (index == targetIndex) break;
+            else if (index < targetIndex) left = index + 1;
+            else right = index - 1;
+        }
+        return nums[targetIndex];
+    }
+    private int partition(int[] nums, int left, int right) {
+        int leftwall = left;
+        int pVal = nums[right];
+        for (int i = left; i < right; i++) {
+            if (nums[i] < pVal) {
+                swap(nums, i, leftwall);
+                leftwall++;
+            }
+        }
+        swap(nums, right, leftwall);
+        return leftwall;
+    }
+    private void swap(int[] nums, int i, int j) {
+        int temp = nums[i];
+        nums[i] = nums[j];
+        nums[j] = temp;
+    }
+}
+```
 
 ## 堆