WA on #3 to #10.

#include <bits/stdc++.h>
using namespace std;

int q, op, x, y, cnt;
struct node {
	int l, r;
} a[1000010];

void insert(int x, int y) {
	a[y].l = x;
	a[y].r = a[x].r;
	a[x].r = y, a[a[y].r].l = y;
}

int nxet(int x) {
	return a[x].r;
}

void pop(int x) {
	a[a[x].l].r = a[x].r;
	a[a[x].r].l = a[x].l;
	a[x] = {0, 0};
}

signed main() {
	cin >> q;
	while (q--) {
		cin >> op;
		if (op == 1) cin >> x >> y, insert(x, y);
		else if (op == 2) cin >> x, cout << nxet(x) << '\n';
		else cin >> x, pop(x);
	}
}