暴力超时代码

#include<iostream>

using namespace std;
const int N = 1e5 + 10;
int a[N];

int main() {
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) scanf("%d", &a[i]);
    printf("-1 ");
    for (int i = 1; i < n; i++) {
        for (int j = i - 1;; j--) {
            if (j >= 0 && a[j] < a[i]) {
                cout << a[j] << " ";
                break;
            } else if (j < 0) {
                cout << "-1 ";
                break;
            }
        }
    }
}

单调栈

#include<iostream>

using namespace std;
const int N = 1e5 + 10;
int stk[N], tt;

int main() {
    int n;
    cin >> n;
    while (n--) {
        int x;
        scanf("%d", &x);
        while (tt && stk[tt] >= x) tt--;
        if (!tt) printf("-1 ");
        else printf("%d ", stk[tt]);
        stk[++tt] = x;
    }
}