獎品的價值 Erasing and Winning

//紫書P253 獎品的價值 
//Serene
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<string>
#include<cstdio>
#include<cmath>
#include<deque>
using namespace std;
const int maxn=1e5+10;
int n,d,r;
int a[maxn];
deque<int> Q;

int aa;char c;
int read() {
	aa=0;c=getchar();
	while(c<'0'||c>'9') c=getchar();
	while(c>='0'&&c<='9') aa=aa*10+c-'0',c=getchar();
	return aa;
}

int main() {
	string g;
	n=read();d=read();
	int pos;
	while(n) {
		getline(cin,g);
		Q.clear();
		for(int i=0;i<g.length();++i) a[i+1]=g[i]-'0';
		Q.push_back(1);pos=1;r=d+1;
		for(int i=1;i<=n-d;++i) {
			while(pos!=r) {
				pos++;
				while(!Q.empty()&&a[Q.back()]<a[pos]) Q.pop_back();
				Q.push_back(pos);
			}
			printf("%d",a[Q.front()]);
			Q.pop_front();r++;
		}
		printf("\n");
		n=read();d=read();
	}
	return 0;
}