HDU 1506Largest Rectangle in a Histogram

http://acm.hdu.edu.cn/showproblem.php?pid=1506解题思路 用l[i]存放a[i]连续的比他大的最左边的数的位置  r[i]存放a[i]连续的比他大的最右边的数的位置a[i]*(r[i]-l[i])就是第i个能得到的最大面积；

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#include<vector>
#include<cmath>
#include<stdlib.h>
#include<iomanip>
#include<list>
#include<deque>
#include<map>
#include <stdio.h>
#include <queue>

#define maxn 100000+5
#define ull unsigned long long
#define ll long long
#define reP(i,n) for(i=1;i<=n;i++)
#define rep(i,n) for(i=0;i<n;i++)
#define cle(a) memset(a,0,sizeof(a))
#define mod 90001
#define PI 3.141592657
#define INF 1<<30
const ull inf = 1LL << 61;
const double eps=1e-5;

using namespace std;

bool cmp(int a,int b){
return a>b;
}
ll a[maxn];
ll l[maxn];
ll r[maxn];
int main()
{
//freopen("in.txt","r",stdin);
//freopen("out.txt","w",stdout);
int n;
while(cin>>n&&n)
{
for(int i=1;i<=n;i++)
scanf("%I64d",&a[i]);
l[1]=1;
r
=n;///记录位置
int t;
for(int i=2;i<=n;i++)
{
t=i;
while(t>1&&a[i]<=a[t-1])t=l[t-1];
l[i]=t;
}
for(int i=n-1;i>=1;i--)
{
t=i;
while(t<n&&a[i]<=a[t+1])t=r[t+1];
r[i]=t;
}
ll Max=0,k;
for(int i=1;i<=n;i++)
{
k=(r[i]-l[i]+1)*a[i];
if(k>Max)
Max=k;
}
printf("%I64d\n",Max);
}

return 0;
}