Submission #1356091

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Source Code Expand

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

const int inf = 1e9;
int n, x, y, rp[200010], rd[200010], bp[200010], bd[200010], ans;
vector<int> re[200010], be[200010];

void T_T(){ puts("-1"); exit(0); }

void f(int t, int x, int pr, int de, int *p, int *d){
	if(!t && bd[x] <= de) return;
	d[x] = de;
	p[x] = pr;
	if(t){
		for(auto &i : be[x]){
			if(i != pr) f(t, i, x, de + 1, p, d);
		}
	}
	else{
		for(auto &i : re[x]){
			if(i != pr) f(t, i, x, de + 1, p, d);
		}
	}
}

int main(){
	scanf("%d%d%d", &n, &x, &y);
	auto in = [](int t){
		for(int i = 0, x, y; i < n - 1; i++){
			scanf("%d%d", &x, &y);
			(t ? be[x] : re[x]).push_back(y);
			(t ? be[y] : re[y]).push_back(x);
		}
	};
	in(0); in(1);
	f(1, y, 0, 0, bp, bd);
	fill(rd + 1, rd + n + 1, inf);
	f(0, x, 0, 0, rp, rd);
	for(int i = 1; i <= n; i++){
		for(auto &j : re[i]){
			int a = i, b = j;
			if(bd[a] > bd[b]) swap(a, b);
			if(bp[b] == a || bp[bp[b]] == a || bp[a] == bp[b]) continue;
			if(bd[a] > rd[a] || bd[b] > rd[b]) T_T();
		}
	}
	for(int i = 1; i <= n; i++) if(rd[i] < inf) ans = max(ans, 2 * bd[i]);
	printf("%d\n", ans);
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:27:29: 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: In lambda function:
./Main.cpp:30:25: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d%d", &x, &y);
                         ^

Judge Result