习题8-4(uva-11491)

#include <iostream>
#include <istream>
#include <sstream>
#include <vector>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
#include <numeric>
#include <chrono>
#include <ctime>
#include <cmath>
#include <cctype>
#include <string>
#include <cstdio>
#include <iomanip>


#include <thread>
#include <mutex>
#include <condition_variable>
#include <functional>
#include <iterator>
using namespace std;
const int maxn = 1e5 + 7;
int n, m;
char input[maxn],q[maxn];

int main()
{
    
    
	while (cin >> n >> m && n && m) {
    
    
		cin >> input;
		int cnt = n - m,tail = 0;
		for (int i = 0; i < n; i++) {
    
    
			int tmp = input[i];
			while (tail && n - i + tail > cnt && tmp > q[tail - 1]) tail--; 
			q[tail++] = tmp;
		}
		q[cnt] = '\0';
		cout <<q <<  endl;
	}
	return 0;
}