Largest Rectangle in a Histogram POJ - 2559

很显然是单调栈

这里记录一种新的写法，这种写法基于递推，但是相比之下比单调栈更好写

#include<cstdio>
#include<map>
#include<set>
#include<queue>
#include<string>
#include<stack>
#include<vector>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
//#define endl "\n"
#define inf 0x3f3f3f3f
#define me(a,b) memset(a,b,sizeof(a))
#define maxn  100000+5
long long n,a[maxn];
int l[maxn],r[maxn];
stack<long long> st;
long long mx;
void init()
{
    mx=;
    while(!st.empty())
        st.pop();
}
int main()
{
    while(cin>>n&&n){
        init();
        for(int i=;i<=n;i++)
            scanf("%I64d",&a[i]),l[i]=r[i]=i;
        a[]=;
        for(int i=;i<=n;i++){
            int now=i;
            while(now>&&a[i]<=a[now-]) now=l[now-];
            l[i]=now;
        }
        for(int i=n-;i;i--){
            int now=i;
            while(now<n&&a[i]<=a[now+]) now=r[now+];
            r[i]=now;
        }
        for(int i=;i<=n;i++)
            mx=max(mx,a[i]*(r[i]-l[i]+));
        cout<<mx<<endl;
    }
}