Submission #3492847

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Source Code Expand

#include<bits/stdc++.h>
#define pii pair<int, int>
using namespace std;
const int N = 2e5 + 10;
const int inf = 0x3f3f3f3f;

int n, E, Ex, X, Y;
int a[N], b[N], c[N], d[N];
int fir[N], nex[N << 1], arr[N << 1], dep[N], fa[N];
int firx[N], nexx[N << 1], arrx[N << 1], tim[N], tag[N];
queue<int> Q;

inline void Add_Edge(int x, int y) {
	nex[++E] = fir[x];
	fir[x] = E; arr[E] = y;
}

inline void Add_Edge2(int x, int y) {
	nexx[++Ex] = firx[x];
	firx[x] = Ex; arrx[Ex] = y;
}

void dfs(int x) {
	for (int i = fir[x]; i; i = nex[i]) {
		if (arr[i] == fa[x]) continue;
		fa[arr[i]] = x;
		dep[arr[i]] = dep[x] + 1;
		dfs(arr[i]);
	}
}

int dis(int x, int y) {
	if (fa[x] == y || fa[y] == x) return 1;
	if (fa[fa[x]] == y || fa[fa[y]] == x || fa[x] == fa[y]) return 2;
	else return 3;
}

void bfs() {
	tim[X] = 0;
	Q.push(X);
	while (!Q.empty()) {
		int x = Q.front(); Q.pop();
		for (int i = firx[x]; i; i = nexx[i]) {
			if (tim[arrx[i]] < inf) continue;
			if (tim[x] + 1 < dep[arrx[i]] && tim[x] + 1 < tim[arrx[i]]) {
				tim[arrx[i]] = tim[x] + 1;
				Q.push(arrx[i]);
			}
		}
	}
	int ans = 0;
	for (int i = 1; i <= n; ++i) {
		if (tim[i] < inf) {
			if (tag[i]) {
				puts("-1");
				exit(0);
			}
			else ans = max(ans, dep[i] * 2);
		}
	}
	cout << ans << endl;
}

int main() {
	scanf("%d%d%d", &n, &X, &Y);
	for (int i = 1; i < n; ++i) {
		scanf("%d%d", &a[i], &b[i]);
	}
	for (int i = 1; i < n; ++i) {
		scanf("%d%d", &c[i], &d[i]);
	}
	for (int i = 1; i < n; ++i) {
		Add_Edge(c[i], d[i]);
		Add_Edge(d[i], c[i]);
	}
	dfs(Y);
	for (int i = 1; i < n; ++i) {
		Add_Edge2(a[i], b[i]);
		Add_Edge2(b[i], a[i]);
		if (dis(a[i], b[i]) == 3) tag[a[i]] = tag[b[i]] = 1;
	}
	memset(tim, 0x3f, sizeof tim);
	bfs();
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:65:29: 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:67:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &a[i], &b[i]);
                              ^
./Main.cpp:70:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &c[i], &d[i]);
                              ^

Judge Result