1250: Rails

http://tjuacm.chaosheng.top/problem.php?id=1250
利用栈，判断是否符合条件。
参考
https://blog.csdn.net/Walton_/article/details/53150777?utm_medium=distribute.pc_relevant_t0.none-task-blog-2%7Edefault%7EBlogCommendFromMachineLearnPai2%7Edefault-1.control&dist_request_id=&depth_1-utm_source=distribute.pc_relevant_t0.none-task-blog-2%7Edefault%7EBlogCommendFromMachineLearnPai2%7Edefault-1.control

#include <iostream>
#include <stack>

using namespace std;

const int MAXN = 1001;

int num[MAXN];

int main(){
    int n;
    while(cin >> n){
        if(n == 0) break;
        while(cin >> num[1]){
            if(num[1] == 0){
                printf("\n");
                break;
            }
            for(int i = 2; i <= n; i++){
                cin >> num[i];
            }
            stack<int> s;
            int a = 1;
            int b = 1;
            bool flag = true;
            while(b <= n){
                if(a == num[b]){
                    a++;
                    b++;
                }else if(!s.empty() && s.top() == num[b]){
                    s.pop();
                    b++;
                }else if(a <= n){
                    s.push(a);
                    a++;
                }else{
                    flag = false;
                    break;
                }
            }
            if(flag){
            printf("Yes\n");
            }else{
            printf("No\n");
            }
        }    
    }
    return 0;
}