Submission #1697385

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Source Code Expand

//2017-10-21
//miaomiao
//
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

#define pb push_back
#define For(i, a, b) for(int i = (a); i <= (int)(b); ++i)
#define Forr(i, a, b) for(int i = (a); i >= (int)(b); --i)

#define LOG 20
#define N (200000+5)

vector<int> G1[N], G2[N];

int n, ans, dep2[N], u1[N], v1[N], f[N][LOG];
bool reach[N];

void Dfs2(int now, int D, int F){
	dep2[now] = D; f[now][0] = F;
	For(i, 1, 18) f[now][i] = f[f[now][i-1]][i-1];

	For(i, 0, G2[now].size()-1)
		if(G2[now][i] != F) Dfs2(G2[now][i], D+1, now);
}

void Dfs1(int now, int D, int F){
	if(dep2[now] <= D) return;
	
	reach[now] = true; ans = max(ans, dep2[now]);
	For(i, 0, G1[now].size()-1)
		if(G1[now][i] != F) Dfs1(G1[now][i], D+1, now);
}

int Dis(int u, int v){
	if(dep2[u] < dep2[v]) swap(u, v);

	int ret = 0;
	Forr(i, 18, 0) if(dep2[f[u][i]] >= dep2[v]){
		ret += 1<<i; u = f[u][i];
	}
	if(u == v) return ret;
	
	Forr(i, 18, 0) if(f[u][i] ^ f[v][i]){
		ret += (1<<i) << 1;
		u = f[u][i]; v = f[v][i];
	}
	return ret + 2;
}

void Check(){
	int u, v;

	For(i, 1, n) ++dep2[i];
	For(i, 1, n-1){
		u = u1[i], v = v1[i];
		if(!reach[u] && !reach[v]) continue;
		if(Dis(u, v) >= 3){puts("-1"); return;}
	}

	printf("%d\n", ans<<1);
}

int main(){
	int st1, st2, u, v;

	scanf("%d%d%d", &n, &st1, &st2);
	
	For(i, 1, n-1){
		scanf("%d%d", &u, &v);
		G1[u].pb(v); G1[v].pb(u);
		u1[i] = u; v1[i] = v;
	}
	For(i, 1, n-1){
		scanf("%d%d", &u, &v);
		G2[u].pb(v); G2[v].pb(u);
	}

	Dfs2(st2, 0, 0); Dfs1(st1, 0, 0);
	Check();

	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:74:33: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d", &n, &st1, &st2);
                                 ^
./Main.cpp:77:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &u, &v);
                        ^
./Main.cpp:82:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &u, &v);
                        ^

Judge Result