堆栈 （LIFO）

数组实现：

#include <stdio.h>
#define N 1000
int main()
{
    int i, n, target[N];
    while(scanf("%d", &n) == 1)
    {
        int stack[N], top = -1;
        for(i = 0; i < n; i++)      scanf("%d", &target[i]);
        int A = 1, B = 0;
        int ok = 1;
        while(B < n)
        {
            if(A == target[B]) { A++;  B++;  }
            else if(top >= 0 && stack[top] == target[B]) {  top--; B++; }
            else if(A <= n) { stack[++top] = A++;  }
            else  {  ok = 0; break;  }
        }
        printf("%s\n", ok ? "Yes" : "No");
    }
    return 0;
}

STL实现：

#include <cstdio>
#include <stack>
#define N 1000
using namespace std;
int main()
{
    int i, n, target[N];
    while(scanf("%d", &n) == 1)
    {
        stack<int> s;
        for(i = 0; i < n; i++)   scanf("%d", &target[i]);
        int A = 1, B = 0, ok = 1;
        while(B < n)
        {
            if(A == target[B]) { A++; B++; }
            else if(!s.empty() && s.top() == target[B]) { s.pop(); B++; }
            else if(A <= n) { s.push(A++);}
            else { ok = 0;  break; }
        }
        printf("%s\n", ok ? "Yes" : "No");
    }
    return 0;
}