Submission #1689689

---

Source Code Expand

#ifdef DEBUG
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <iostream>
#include <cassert>
#include <sstream>
#include <fstream>
#include <functional>
#include <set>
#include <bitset>
#include <string>
#include <utility>
#include <queue>
#include <deque>
#include <vector>
#include <map>
#else
#include <bits/stdc++.h>
#endif

#ifdef DEBUG
#define debug(...) fprintf(stderr, __VA_ARGS__)
#else
#define debug(...)
#endif

#define rep(i, n) for (int i = 0, i##_end_ = (n); i < i##_end_; ++i)
#define per(i, n) for (int i = (n) - 1; i >= 0; --i)
#define forn(i, l, r) for (int i = (l), i##_end_ = (r); i <= i##_end_; ++i)
#define nrof(i, r, l) for (int i = (r), i##_end_ = (l); i >= i##_end_; --i)
#define X first
#define Y second
#define mp make_pair
#define pb push_back
#define SZ(x) (int)((x).size())
#define ALL(x) (x).begin(), (x).end()

using namespace std;

typedef vector<int> vi;

typedef pair<int, int> pii;

typedef long long LL;

template<typename T> inline bool chkmax(T &x, const T &y) {
	return (x < y && x != -1) ? x = y, 1 : 0;
}

template<typename T> inline bool chkmin(T &x, const T &y) {
	return x > y ? x = y, 1 : 0;
}

#ifdef DEBUG
char *input_file, *output_file;
#endif

struct IO {
	static const int maxn = (1 << 25) + 10;

	char a[maxn], *s, b[maxn], *t;

	void INPUT() {
		s = a;
		t = b;
		#ifdef DEBUG
		FILE *f = fopen(input_file, "r");
		a[fread(a, 1, sizeof a, f)] = 0;
		#else
		a[fread(a, 1, sizeof a, stdin)] = 0;
		#endif
	}

	void OUTPUT() {
#ifdef DEBUG
		FILE *f = fopen(output_file, "w");
		fwrite(b, 1, t - b, f);
#else
		fwrite(b, 1, t - b, stdout);
#endif
	}

	operator int() {
		int x = 0;
		while(*s != '-' && (*s < '0' || *s > '9')) {
			++s;
		}
		bool f = 0;
		if(*s == '-') {
			f = 1;
			++s;
		}
		while(*s >= '0' && *s <= '9') {
			(x *= 10) += *s - '0';
			++s;
		}
		if(f) {
			x = -x;
		}
		return x;
	}

	operator LL() {
		LL x = 0;
		while(*s != '-' && (*s < '0' || *s > '9')) {
			++s;
		}
		bool f = 0;
		if(*s == '-') {
			f = 1;
			++s;
		}
		while(*s >= '0' && *s <= '9') {
			(x *= 10) += *s - '0';
			++s;
		}
		if(f) {
			x = -x;
		}
		return x;
	}

	operator char() {
		while(*s <= 32) {
			++s;
		}
		char ret = *s;
		++s;
		return ret;
	}

	inline void out(int x) {
		if(!x) {
			*t++ = '0';
			return;
		}
		if(x < 0) {
			*t++ = '-';
			x = -x;
		}
		static char c[20], *i;
		i = c;
		while(x) {
			int y = x / 10;
			*i++ = x - y * 10 + '0';
			x = y;
		}
		while(i != c) {
			*t++ = *--i;
		}
		return;
	}

	inline void out(int x, char C) {
		if(!x) {
			*t++ = '0';
			*t++ = C;
			return;
		}
		if(x < 0) {
			*t++ = '-';
			x = -x;
		}
		static char c[20], *i;
		i = c;
		while(x) {
			int y = x / 10;
			*i++ = x - y * 10 + '0';
			x = y;
		}
		while(i != c) {
			*t++ = *--i;
		}
		*t++ = C;
		return;
	}

	inline void out(LL x) {
		if(!x) {
			*t++ = '0';
			return;
		}
		if(x < 0) {
			*t++ = '-';
			x = -x;
		}
		static char c[20], *i;
		i = c;
		while(x) {
			LL y = x / 10;
			*i++ = x - y * 10 + '0';
			x = y;
		}
		while(i != c) {
			*t++ = *--i;
		}
		return;
	}

	inline void out(LL x, char C) {
		if(!x) {
			*t++ = '0';
			*t++ = C;
			return;
		}
		if(x < 0) {
			*t++ = '-';
			x = -x;
		}
		static char c[20], *i;
		i = c;
		while(x) {
			LL y = x / 10;
			*i++ = x - y * 10 + '0';
			x = y;
		}
		while(i != c) {
			*t++ = *--i;
		}
		*t++ = C;
		return;
	}

	inline void out(char c) {
		*t++ = c;
		return;
	}

	inline void out(char *s) {
		while(*s >= ' ') {
			*t++ = *s++;
		}
		return;
	}
}io;

void Main();

int main(int argc, char *argv[]) {
#ifdef DEBUG
	input_file = argv[1];
	output_file = argv[2];
#endif
	io.INPUT();
	Main();
	io.OUTPUT();
	return 0;
}

//---------------------------------------------------------------------------------------head---------------------------------------------------------------------------------------

const int maxn = 2e5 + 100;

const int lgn = 19;

int n, r1, r2, ans;
vi g1[maxn], g2[maxn];
int par1[maxn][lgn], par2[maxn][lgn];
int dep1[maxn], dep2[maxn];

void dfs1(int u = r1, int p = 0) {
	par1[u][0] = p;
	forn(i, 1, lgn - 1) {
		par1[u][i] = par1[par1[u][i - 1]][i - 1];
	}
	dep1[u] = dep1[p] + 1;
	for (int v: g1[u]) {
		if(v != p) {
			dfs1(v, u);
		}
	}
	return;
}

void dfs2(int u = r2, int p = 0) {
	par2[u][0] = p;
	forn(i, 1, lgn - 1) {
		par2[u][i] = par2[par2[u][i - 1]][i - 1];
	}
	dep2[u] = dep2[p] + 1;
	for (int v: g2[u]) {
		if(v != p) {
			dfs2(v, u);
		}
	}
	return;
}

int lca(int u, int v) {
	if(dep2[u] < dep2[v]) {
		swap(u, v);
	}
	int dlt = dep2[u] - dep2[v];
	rep(i, lgn) {
		if((dlt >> i) & 1) {
			u = par2[u][i];
		}
	}
	if(u == v) {
		return u;
	}
	per(i, lgn) {
		if(par2[u][i] != par2[v][i]) {
			u = par2[u][i], v = par2[v][i];
		}
	}
	return par2[u][0];
}

void dfs3(int u = r1, int p = 0) {
	chkmax(ans, dep2[u] - 1 << 1);
	if(dep1[u] >= dep2[u]) {
		return;
	}
	if(p) {
		int f = lca(u, p);
		if(dep2[u] + dep2[p] - dep2[f] * 2 > 2) {
			ans = -1;
			return;
		}
	}
	for (int v: g1[u]) {
		if(v != p) {
			dfs3(v, u);
		}
	}
	return;
}

void Main() {
	n = io;
	r1 = io;
	r2 = io;
	rep(i, n - 1) {
		int u = io, v = io;
		g1[u].pb(v);
		g1[v].pb(u);
	}
	rep(i, n - 1) {
		int u = io, v = io;
		g2[u].pb(v);
		g2[v].pb(u);
	}
	dfs1();
	dfs2();
	dfs3();
	io.out(ans, '\n');
	return;
}

Submission Info

Judge Result