题解 | #寻找第K大#

#include <vector>
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param a int整型vector
     * @param n int整型
     * @param K int整型
     * @return int整型
     */

    int partition(vector<int>& vec, int l, int r) {
        int pivot = vec[l];
        int i = l + 1;
        for (int j = l + 1; j <= r; j++) {
            if (vec[j] >= pivot)
                swap(vec[j], vec[i++]);
        }
        swap(vec[l], vec[i - 1]);
        return i - 1;
    }
    int findKth(vector<int>& a, int n, int K) {
        // write code here
        int res;
        if (n == 0) return -1;
        int left = 0, right = n-1;
        while (left <= right) {
            int index = partition(a, left, right);
            if (index + 1 == K) {
                return a[index];
            } else if (index + 1 < K) {
                left = index + 1;
            } else {
                right = index - 1; 
            }
        }
        return -1;
    }
};