BZOJ 1660 乱发节

单调栈。ans开long long。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 80050
using namespace std;
int n,a[maxn],stack[maxn],top=0;
long long ans=0;
int main()
{
    scanf("%d",&n);for (int i=1;i<=n;i++) scanf("%d",&a[i]);
    for (int i=n;i>=1;i--)
    {
        while ((top) && (a[i]>a[stack[top]]))
            top--;
        if (top) ans+=stack[top]-i-1;
        else ans+=n-i;
        stack[++top]=i;
    }    
    printf("%lld\n",ans);
    return 0;
}