215. 数组中的第K个最大元素 - 力扣（LeetCode） (leetcode-cn.com)
     自己写的代码
     public class Solution1 {
     public int findKthLargest(int[] nums,int k){//{3,2,1,5,6,4},2
     int hideCode = nums.length;
     findLargest(nums,hideCode);
     for(int i=nums.length-1;i>=nums.length-k+1;--i){
     swap(nums,0,i);
     --hideCode;
     findLargest(nums,hideCode);
     }
     return nums[0];
     }
     public void findLargest(int[] nums,int hideCode){//{3,2,1,5,6,4},2
     for (int i=hideCode/2;i>=0;--i){
     Largest(nums,i,hideCode);
     }
     }
     public void Largest(int[] nums,int i,int hideCode){//{3,2,1,5,6,4},2
     int l=i2+1,r=i2+2,largest=i;
     if (l<hideCode && nums[l]>nums[largest]){
     largest = l;
     }
     if (r<hideCode && nums[r]>nums[largest]){
     largest = r;
     }
     if (largest != i){
     swap(nums,i,largest);
     Largest(nums,largest,hideCode);
     }
     }
     public void swap(int[] nums,int pass,int now){
     int temp = nums[pass];
     nums[pass] = nums[now];
     nums[now] = temp;
     }
     答案代码
     public class RuleSolution {
     public int findKthLargest(int[] nums, int k) {
     int heapSize = nums.length;
     buildMaxHeap(nums, heapSize);
     for (int i = nums.length - 1; i >= nums.length - k + 1; --i) {
     swap(nums, 0, i);
     --heapSize;
     maxHeapify(nums, 0, heapSize);
     }
     return nums[0];
     }

public void buildMaxHeap(int[] a, int heapSize) {

    for (int i = heapSize / 2; i >= 0; --i) {
        maxHeapify(a, i, heapSize);
    }
}

public void maxHeapify(int[] a, int i, int heapSize) {
    int l = i * 2 + 1, r = i * 2 + 2, largest = i;
    if (l < heapSize && a[l] > a[largest]) {
        largest = l;
    }
    if (r < heapSize && a[r] > a[largest]) {
        largest = r;
    }
    if (largest != i) {
        swap(a, i, largest);
        maxHeapify(a, largest, heapSize);
    }
}

public void swap(int[] a, int i, int j) {
    int temp = a[i];
    a[i] = a[j];
    a[j] = temp;
}

}