leetcode_找到第 k 大的元素

排序

class Solution {
    public int findKthLargest(int[] nums, int k) {
        Arrays.sort(nums);
        return nums[nums.length-k];
    }
}

 

利用小根堆

class Solution {
    public int findKthLargest(int[] nums, int k) {
        PriorityQueue<Integer> minHeap = new PriorityQueue<>();
        for(int num:nums){
            minHeap.add(num);
            if(minHeap.size()>k) minHeap.poll();
        }
        return minHeap.peek();
    }
}

 

快速排序

public int findKthLargest(int[] nums, int k) {
k = nums.length - k;
int l = 0, h = nums.length - 1;
while (l < h) {
int j = partition(nums, l, h);
if (j == k) {
break;
} else if (j < k) {
l = j + 1;
} else {
h = j - 1;
}
}
return nums[k];
}
private int partition(int[] a, int l, int h) {
int i = l, j = h + 1;
while (true) {
while (a[++i] < a[l] && i < h) ;
while (a[--j] > a[l] && j > l) ;
if (i >= j) {
break;
}
swap(a, i, j);
}
swap(a, l, j);
return j;
}
private void swap(int[] a, int i, int j) {
int t = a[i];
a[i] = a[j];
a[j] = t;
}