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Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.
For example,
Given [3,2,1,5,6,4] and k = 2, return 5.
Note:
You may assume k is always valid, 1 ≤ k ≤ array‘s length.
最简单的想法：先排序，然后倒数k个元素就是
时间复杂度：O(nlogn)
public class Solution { public int findKthLargest(int[] nums, int k) { Arrays.sort(nums); return nums[nums.length-k]; } }
优化：quicksort 中 partition 的思想
就像quickselect一样，时间复杂度应该是 O(n)
public class Solution { public int findKthLargest(int[] nums, int k) { return helper(nums, 0, nums.length-1, k); } public int helper(int[] nums, int lo, int hi, int k) { // if (lo == hi) // return nums[lo]; int partition = nums[lo]; int j = hi; for (int i = lo+1; i <= j;) { while (i <= hi && nums[i] < partition) i++; while (j >= lo && nums[j] > partition) j--; if (i <= j) { swap(nums, i, j); i++; j--; } } swap(nums, j, lo); if (k == hi - j + 1) return nums[j]; if (k < hi - j + 1) return helper(nums, j + 1, hi, k); else return helper(nums, lo, j - 1, k - (hi - j + 1)); } public void swap(int[] nums, int i, int j) { int temp = nums[i]; nums[i] = nums[j]; nums[j] = temp; } }
2015-10-21
LeetCode 215 : Kth Largest Element in an Array
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原文地址：http://www.cnblogs.com/whuyt/p/4898495.html
