Codeforces 319B. Psychos in a Line【栈】

#include <iostream>
#include <cstdio>
#define N 100010
using namespace std;
int a[N];
int ans,n;
struct aa
{
    int x,eat;
}que[N];
int main()
{
    int tail=0;
    scanf("%d",&n);
    for(int i=0;i<n;i++)
        scanf("%d",a+i);
    int i=1;
    while(a[i-1]<a[i] && i<n) i++;
    que[tail].x=a[i-1],que[tail++].eat=0;
    for(;i<n;i++)
    {
        if(a[i]<que[tail-1].x)
        {
            que[tail].x=a[i],que[tail++].eat=1;
            ans=max(ans,que[tail-1].eat);
            continue;
        }
        int ma=0;
        while(tail>0 && a[i]>que[tail-1].x) ma=max(ma,que[tail-1].eat),tail--;
        if(tail==0) que[tail].eat=0;
        else que[tail].eat=ma+1;
        que[tail++].x=a[i];
        ans=max(ans,que[tail-1].eat);
    }

    cout<<ans<<endl;
    return 0;
}