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Leetcode0215.java
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Leetcode0215.java
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package com.y2018.m11.d30;
/**
* Created by zhangweilong on 2019/11/30
*
* @author zhangweilong@corp.netease.com
* @since 2019/11/30
*/
public class Leetcode0215 {
public int findKthLargest(int[] nums, int k) {
//kth largest -> n + 1 - k small
int kth = nums.length + 1 - k;
int l = 0;
int r = nums.length - 1;
while (true) {
int index = sweep(nums, l, r);
//在nums[index]左边的数都比nums[index]小 右边都>=nums[index]
//小于a[index]的个数
int lessAIndex = index - l;
//0-base
if (kth == lessAIndex + 1) {
return nums[index];
}
if (kth <= lessAIndex) {
//在左边部分找[0, index - 1]继续找第kth小的
r = index - 1;
} else {
//在右边部分找[index + 1, r]继续找kth - index -1小的, 因为在nums[index]左边有lessAIndex个数字(0-base), 已经过滤掉了lessAIndex个数字
l = index + 1;
kth = kth - lessAIndex - 1;
}
}
}
//对数组a[l, l+1, l+2, ..., r]扫描,最后比a[l]小的都在a[l]左边, 大于等于a[l]都在右边, 最后返回的结果是a[l]这个数字最后所在位置的下标
private int sweep(int[] a, int l, int r) {
int sentry = a[l];
while (l < r) {
while (a[r] >= sentry && r > l) r--;
if (l < r) swap(a, r, l);
while (a[l] < sentry && l < r) l++;
if (l < r) swap(a, l, r);
}
return l;
}
void swap(int[] a, int x, int y) {
int t = a[x];
a[x] = a[y];
a[y] = t;
}
}