acwing830. 单调栈

#include<iostream>
using namespace std;
const int N=1e5+10;
int sk[N],top;

int main(){
    int n;cin>>n;
    while(n--){
        int x;cin>>x;
        while(top&&sk[top]>=x)top--;
        if(!top)cout<<"-1"<<" ";
        else cout<<sk[top]<<" ";
        sk[++top]=x;
    }
    return 0;
}