这道题是

P8600 [蓝桥杯 2013 省 B] 连号区间数

的前置知识

#include <iostream>
#include <stdio.h>
#include <algorithm>
#include <string>
#include <cmath>
#define R(x) x = read()
#define For(i, j, n) for(int i = j ; i <= n ; ++i)
using namespace std;

inline int read()
{
    int x = 0, f = 1; char ch = getchar();
    while(ch < '0' || ch > '9')
    {
        if(ch == '-') f = -1;
        ch = getchar();
    }
    while(ch >= '0' && ch <= '9')
    {
       x = x * 10 + ch - '0';
       ch = getchar();
    }
     return x * f;
}

const int N = 1e5 + 5;
int n, a[N];
int top, stk[N];

int main()
{
    R(n);
    for(int i = 1; i <= n; i++)
        R(a[i]);
    for(int i = 1; i <= n; i++)
    {
        while(top && stk[top] >= a[i])
            top--;
        if(!top) printf("-1 ");
        else printf("%d ", stk[top]);
        stk[++top] = a[i];
    }
    return 0;
}