uva 11491 Erasing and Winning 奖品的价值 (单调队列)

#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<vector>
using namespace std;

#define all(x) (x).begin(), (x).end()
#define for0(a, n) for (int (a) = 0; (a) < (n); (a)++)
#define for1(a, n) for (int (a) = 1; (a) <= (n); (a)++)
typedef long long ll;
typedef pair<int, int> pii;
const int INF =0x3f3f3f3f;
const int maxn= 100000  ;

int n,d,V;
char s[maxn+10];
bool vis[maxn+10];
int q[maxn+10];
int main()
{
while(~scanf("%d%d",&n,&d)&&(n||d))
{
scanf("%s",s+1);
V=n-d;
memset(vis,0,(n+1)*sizeof vis[0]);
int rear=1,front=1;
for(int i=1;i<=n-V;i++ )
{
while(rear-front>0&&s[q[rear-1]]<s[i]  ) rear--;
q[rear++]=i;
}
for(int i=n-V+1;i<=n;i++)
{
while(rear-front>0&&s[q[rear-1]]<s[i]  ) rear--;
q[rear++]=i;

int x=q[front];
vis[x]=1;
front++;
}
for(int i=1;i<=n;i++) if(vis[i])
{
putchar(s[i]);
}
putchar('\n');

}

return 0;
}