C++60分TLE，求助大佬

#include <bits/stdc++.h>
using namespace std;

int a[5000000];
map <int, int> check;

int findKth (int a[], int len, int key) {
	for (int i = 0; i < len; i++)
		check[a[i]]++;
	int index = 0;
	for (auto p : check) {
		for (int i = 1; i <= p.second; i++) {
			if (index == key)
				return p.first;
			a[index++] = p.first;
		}
	}
}

int main() {
	int n, key;
	cin >> n >> key;
	for (int i = 0; i < n; i++)
		cin >> a[i];
	cout << findKth (a, n, key) << endl;
	return 0;
}