qscoj#19D(单调队列)

题目链接：http://qscoj.cn/problem/130/

题意：中文题诶～

思路：直接用单调栈搞一下就好了

代码：

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

const int MAXN=1e6+10;
const int inf=1e9;
int sum[MAXN], q[MAXN];

int main(void){
    int n, k;
    while(scanf("%d%d", &n, &k)!=EOF){
        for(int i=1; i<=n; i++){
            int x;
            scanf("%d", &x);
            sum[i]=sum[i-1]+x;
        }
        sum[n+1]=-inf;
        int ans=0, front=0, rear=0;
        for(int i=1; i<=n+1; i++){
            ans=max(ans, sum[i]);
            if((front==rear||sum[i]>sum[q[front]])){
                if(i-q[rear+1]+1<k){
                    q[++front]=i;
                }else{
                    while(i-q[rear+1]+1>=k&&front>rear){
                        rear++;
                    }
                    q[++front]=i;
                }
            }else if(sum[i]<sum[q[front]]){
                while(front>rear&&sum[i]<sum[q[front]]){
                    ans=max(ans, sum[q[front]]-sum[q[rear+1]]);
                    front--;
                }
                while(i-q[rear+1]+1>=k&&front>rear){
                    rear++;
                }
                q[++front]=i;
            }
        }
        printf("%d
", ans);
    }
    return 0;
}