Submission #1817926

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Source Code Expand

#include <iostream>
#include <cstdio>
#include <set>
#include <vector>
#include <algorithm>
#define rep(i,a,b) for(int i = a; i <= b; i++)
#define Rep(i,a) for(int i = 0; i < a; i++)
using namespace std;
const int N = 1e5 + 10;

struct edge{ int to, pre; } e[N << 1]; int l = 0, u[N];
void ins(int a, int b) { e[++l] = (edge){b, u[a]}, u[a] = l; }
#define v e[i].to
#define reg(i,a) for(int i = u[a]; i; i = e[i].pre)

int n, X, Y, a[N], b[N], dep[N], fa[N];

void dfs(int x, int f) {
	reg(i,x) if (v != f) dep[v] = dep[x] + 1, fa[v] = x, dfs(v, x);
}

bool jump(int a, int b) {
	if (dep[a] < dep[b]) swap(a, b);
	if (fa[a] == b || fa[fa[a]] == b || fa[a] == fa[b]) return false;
	else return true;
}

vector<int> adj[N];
#define pb(a) push_back(a)

bool inf = false, win[N];
int ans = 0;
void chk(int x, int f, int d) {
	if (d >= dep[x]) return; else ans = max(ans, dep[x]);
	inf |= win[x]; int l = adj[x].size();
	Rep(j,l) if (adj[x][j] != f) chk(adj[x][j], x, d + 1);
}

int main() {
	scanf("%d%d%d",&n,&X,&Y);
	rep(i,1,n - 1) scanf("%d%d",a + i,b + i);
	rep(i,1,n - 1) {
		int a, b; scanf("%d%d",&a,&b);
		ins(a, b), ins(b, a);
	}
	dfs(Y, 0);
	rep(i,1,n - 1) 
		if (!jump(a[i], b[i])) 
			adj[a[i]].pb(b[i]), adj[b[i]].pb(a[i]);
		else win[a[i]] = win[b[i]] = true;
	chk(X, 0, 0);
	if (inf) printf("-1\n");
	else printf("%d\n",ans * 2);
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:40:26: 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:41:42: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  rep(i,1,n - 1) scanf("%d%d",a + i,b + i);
                                          ^
./Main.cpp:43:32: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   int a, b; scanf("%d%d",&a,&b);
                                ^

Judge Result