BZOJ 1657 奶牛的歌声

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 50050
using namespace std;
int n,v[maxn],h[maxn],s[maxn],ans[maxn],t=0;
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++) scanf("%d%d",&h[i],&v[i]);
    for (int i=1;i<=n;i++)
    {
        while (t && h[i]>h[s[t]]) ans[i]+=v[s[t--]];
        s[++t]=i;
    }
    t=0;
    for (int i=n;i>=1;i--)
    {
        while (t && h[i]>h[s[t]]) ans[i]+=v[s[t--]];
        s[++t]=i;
    }
    int mx=0;
    for (int i=1;i<=n;i++) mx=max(mx,ans[i]);
    printf("%d\n",mx);
    return 0;
}