Submission #1857264

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Source Code Expand

#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;

#define iter(i, n) for (int i = 1; i <= n; ++i)
#define iter_d0(i, n) for (int i = n - 1; i >= 0; --i)

const int inf = 1e9;
const int NR = 2e5 + 10;

int n, X, Y, xa[NR], ya[NR], fa[NR], f[NR][20], dep[NR];
vector<int> Ta[NR], Tb[NR];

void dfs(int x) {
	f[x][0] = fa[x];
	for (int i = 1; (1 << i) <= dep[x]; ++i)
		f[x][i] = f[f[x][i - 1]][i - 1];
	for (int v : Tb[x]) if (v != fa[x]) {
		fa[v] = x, dep[v] = dep[x] + 1, dfs(v);
	}
}

int lca(int x, int y) {
	if (dep[x] < dep[y]) swap(x, y);
	iter_d0(i, 20) if (dep[f[x][i]] >= dep[y]) x = f[x][i];
	if (x == y) return x;
	iter_d0(i, 20) if (f[x][i] != f[y][i]) x = f[x][i], y = f[y][i];
	return fa[x];
}

int dist(int x, int y) {
	return dep[x] + dep[y] - 2 * dep[lca(x, y)];
}

int getans(int x, int fa, int d) {
	int res = dist(x, Y); //printf("!!%d\n", x);
	for (int v : Ta[x]) if (v != fa) {
		//printf("!%d %d\n", v, dist(v, Y));
		if (dist(x, v) >= 3) return inf;
		if (dep[v] > d + 1)
			res = max(res, getans(v, x, d + 1));
	}
	return res;
}

int main() {
	//freopen("5E.in", "r", stdin);
	scanf("%d%d%d", &n, &X, &Y); dep[0] = -1;
	iter(i, n - 1) {
		scanf("%d%d", &xa[i], &ya[i]);
		Ta[xa[i]].push_back(ya[i]);
		Ta[ya[i]].push_back(xa[i]);
	}
	iter(i, n - 1) {
		int x, y;
		scanf("%d%d", &x, &y);
		Tb[x].push_back(y);
		Tb[y].push_back(x);
	}

	dfs(Y);
	int tmp = getans(X, 0, 0);
	printf("%d\n", tmp == inf ? -1 : 2 * tmp);
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:49:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d", &n, &X, &Y); dep[0] = -1;
                             ^
./Main.cpp:51:32: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &xa[i], &ya[i]);
                                ^
./Main.cpp:57:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &x, &y);
                        ^

Judge Result