Submission #1593800

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Source Code Expand

#include <bits/stdc++.h>

typedef long long ll;
typedef long long llong;
typedef long double ld;
typedef unsigned long long ull;

using namespace std;

/*
ll pw(ll a, ll b) {
	ll ans = 1; while (b) {
		while (!(b & 1)) b >>= 1, a = (a * a) % MOD;
		ans = (ans * a) % MOD, --b;
	} return ans;
}
*/
const int MAXN = 220000;
int n;
int was[MAXN];
int h[MAXN];
int p[MAXN];
vector<int> eds0[MAXN];
vector<int> eds1[MAXN];
int dd[MAXN];
queue<int> qu;

void dfs1(int v) {
	was[v] = 1;
	for (int u: eds1[v]) {
		if (was[u])
			continue;
		p[u] = v;
		h[u] = h[v] + 1;
		dfs1(u);
	}
}

int dst(int a, int b) {
	if (a == b)
		return 0;
	if (p[a] == b || p[b] == a)
		return 1;
	if (p[a] == p[b] || (p[a] != -1 && p[p[a]] == b) || (p[b] != -1 && p[p[b]] == a))
		return 2;
	return 3;
}

int main() {
	int x, y;
	int ans = 0;
	scanf("%d%d%d", &n, &x, &y);
	--x, --y;
	for (int i = 0; i < n - 1; ++i) {
		int a, b;
		scanf("%d%d", &a, &b);
		--a, --b;
		eds0[a].push_back(b);
		eds0[b].push_back(a);
	}
	for (int i = 0; i < n - 1; ++i) {
		int a, b;
		scanf("%d%d", &a, &b);
		--a, --b;
		eds1[a].push_back(b);
		eds1[b].push_back(a);
	}
	dfs1(y);
	p[y] = -1;
	
	qu.push(x);
	for (int i = 0; i < n; ++i)
		dd[i] = -1;
	dd[x] = 0;
	while (!qu.empty()) {
		int x = qu.front();
		qu.pop();
		ans = max(ans, h[x] * 2);
		if (dd[x] < h[x]) {
			for (int u: eds0[x]) {
				if (dst(x, u) > 2) {
					cout << -1 << "\n";
					return 0;
				}
				if (dd[u] == -1)
					dd[u] = dd[x] + 1, qu.push(u);
			}
		}
	}
	cout << ans << "\n";
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:52:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d", &n, &x, &y);
                             ^
./Main.cpp:56:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &a, &b);
                        ^
./Main.cpp:63:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &a, &b);
                        ^

Judge Result