建议加强数据

#include <bits/stdc++.h>
using namespace std;
#define il inline
const int N = 1e5 + 10;
int idx[N], pre[N], nxt[N], v[N], n;
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	cin >> n;
	for(int i = 1;i <= n;++i)
	{
		cin >> v[i];
		idx[v[i]] = i;
		pre[i] = i - 1;
		nxt[i] = i + 1;
	}
	nxt[n] = 0;
	for(int i = n;i >= 1;--i)
	{
		if(!v[idx[i]]) continue;
		int j = idx[i] + 1;
		while(j <= n && v[j] == 0) j++;
		if(j > n || v[j] == 0) continue;
		cout << i << " " << v[j] << " ";
		v[idx[i]] = v[j] = 0;
	}
	return 0;
}