算法入门经典P140（stack）

#include<iostream>
using namespace std;
#include<stack>
#include<cstdio>
const int maxn = 1000+5;
int a[maxn];
int main(){
    int n;
    scanf("%d",&n);//3
    stack<int>s;
    int A = 1,B = 1;//A为进站，B为出站 
    for(int i=1;i<=n;i++){//3 1 2
        scanf("%d",&a[i]);
    }
    int ok = 1;
    while(B<=n){
        if(A==a[B]){A++;B++;}
        else if(!s.empty()&&s.top()==a[B]){s.pop();B++;}
        else if(A<=n){s.push(A++);}//s.push(1);A=2;  s.push(2);A=3;
        else{ok = 0;break;}
    }
    printf("%s\n",ok?"Yes":"No");
    return 0;
}