215. 数组中的第K个最大元素

  1. class Solution {
  2.     public int findKthLargest(int[] nums, int k) {
  3.         int heapSize = nums.length;
  4.         buildMaxHeap(nums, heapSize);
  5.         for (int i = nums.length - 1; i >= nums.length - k + 1; --i) {
  6.             swap(nums, 0, i);
  7.             --heapSize;
  8.             maxHeapify(nums, 0, heapSize);
  9.         }
  10.         return nums[0];
  11.     }
  13.     public void buildMaxHeap(int[] a, int heapSize) {
  14.         for (int i = heapSize / 2; i >= 0; --i) {
  15.             maxHeapify(a, i, heapSize);
  16.         } 
  17.     }
  19.     public void maxHeapify(int[] a, int i, int heapSize) {
  20.         int l = i * 2 + 1, r = i * 2 + 2, largest = i;
  21.         if (l < heapSize && a[l] > a[largest]) {
  22.             largest = l;
  23.         } 
  24.         if (r < heapSize && a[r] > a[largest]) {
  25.             largest = r;
  26.         }
  27.         if (largest != i) {
  28.             swap(a, i, largest);
  29.             maxHeapify(a, largest, heapSize);
  30.         }
  31.     }
  33.     public void swap(int[] a, int i, int j) {
  34.         int temp = a[i];
  35.         a[i] = a[j];
  36.         a[j] = temp;
  37.     }
  38. }
  40. 作者：LeetCode-Solution
  41. 链接：https://leetcode-cn.com/problems/kth-largest-element-in-an-array/solution/shu-zu-zhong-de-di-kge-zui-da-yuan-su-by-leetcode-/