POJ-2559 Largest Rectangle in a Histogram(单调栈)

#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <queue>
#include <stack>
#include <vector>
#include <iostream>
#include "algorithm"
using namespace std;
typedef long long LL;
const int MAX=100005;
LL n;
struct Node{
    LL x;
    LL y;
}sta[MAX];
LL h[MAX],ans;
int main(){
    freopen ("histogram.in","r",stdin);
    freopen ("histogram.out","w",stdout);
    int i,j;
    LL zt;
    while (scanf("%lld",&n),n!=0){
        ans=0;
        for (i=1;i<=n;i++){
            scanf("%lld",h+i);
        }
        int top;
        top=1;
        sta[0].x=0,sta[0].y=0;
        sta[top].x=1;
        sta[top].y=h[1];
        for (i=2;i<=n;i++){
            if (h[i]>=sta[top].y){
                sta[++top].y=h[i];
                sta[top].x=i;
            }
            else{
                while (top>0 && h[i]<sta[top].y){
                    zt=((i-1)-sta[top-1].x)*sta[top].y;
                    ans=max(ans,zt);
                    top--;
                }
                sta[++top].x=i;
                sta[top].y=h[i];
            }
        }
        for (i=1;i<=top;i++){
            ans=max(sta[i].y*(sta[top].x-sta[i-1].x),ans);
        }
        printf("%lld\n",ans);
    }
    return 0;
}