有没有大佬知道为什么我第一个空总是过不了啊

#include <bits/stdc++.h>
using namespace std;
bool a[101][101];

struct node {
	int s;
	int d;
};

int main() {
	int n;
	cin >> n;
    if (n==1) {
        cout<<1<<endl;
        cout<<1<<endl;
        cout<<0;
        return 0;
        
    }
	for (int i = 0; i < n - 1; i++) {
		int u, b;
		cin >> u >> b;
		a[u][b] = 1;
	}

	int num = 0;
	int dn[1005] = {};
	node q;
	q.s = 1;
	q.d = 1;
	queue <node> b;
	b.push(q);
	int x, y;
	cin >> x >> y;

	while (num < n) {
		dn[b.front().d]++;
		num++;

		for (int i = 1; i <= n; i++) {
			if (a[b.front().s][i]) {
				q.s = i;
				q.d = b.front().d + 1;
				b.push(q);
			}
		}

		b.pop();
	}

	cout << q.d << endl;
	int ans = -1;

	for (int i = 0; i < 1005; i++) {
		ans = max(ans, dn[i]);
	}

	cout << ans << endl;
	bool step[1005];
	queue <node> b2;

	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			if (a[i][j]) {
				a[j][i] = 1;
			}

		}
	}

	/*
	for (int i = 1; i <= n; i++) {
		cout << endl;

		for (int j = 1; j <= n; j++) {
			cout << a[i][j] << ' ';

		}


	}
	*/
	q.s = x;
	q.d = 0;
	b2.push(q);
	step[x] = 1;


	while (b2.front().s != y) {

		for (int i = 1; i <= n; i++) {
			if (a[b2.front().s][i] && !step[i]) {
				step[i] = 1;
				q.s = i;


				if (b2.front().s > i)
					q.d = b2.front().d + 2;
				else
					q.d = b2.front().d + 1;

				b2.push(q);
			}
		}


		b2.pop();
	}

	cout << b2.front().d;
	return 0;
}