20190107

code/lc215.java

+package code;
+/*
+ * 215. Kth Largest Element in an Array
+ * 题意：找第k大的数
+ * 难度：Medium
+ * 分类：Divide and Conquer, Heap
+ * 思路：快排的思想
+ * Tips：经典的题目，记一下代码格式，方便快速写出
+ */
+public class lc215 {
+    public static void main(String[] args) {
+        int[] nums = {3,2,3,1,2,4,5,5,6};
+        System.out.println(findKthLargest(nums, 4));
+    }
+    public static int findKthLargest(int[] nums, int k) {
+        return quickSort(nums, 0, nums.length-1, k);
+    }
+
+    public static int quickSort(int[] nums, int left, int right, int k){
+        int origin_l = left;        //left 和 right 移动，但要保存一下原始的值，方便递归调用
+        int origin_r = right;
+        int cur = nums[left];
+        while(left<right) {
+            while (left<right && nums[right] < cur)
+                right--;
+            nums[left] = nums[right];
+            while (left<right && nums[left] >= cur)
+                left++;
+            nums[right] = nums[left];
+        }
+        nums[left] = cur;
+        if(left==k-1)
+            return cur;
+        else if(left>k-1)
+            return quickSort(nums, origin_l, left-1, k);
+        else
+            return quickSort(nums, left+1, origin_r, k);
+    }
+}