Submission #3923583

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Source Code Expand

#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-3;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
typedef pair<ld, ld> LDP;

int n;
vector<int> G[1 << 17];
bool exi[1 << 17];

bool used[1 << 17];
int root;
string c;
bool maketree(int id) {
	used[id] = true;
	bool res = false;
	rep(i, G[id].size()) {
		int to = G[id][i];
		if (used[to])continue;
		if (maketree(to))res = true;
	}
	if (c[id] == 'W')res = true;
	if (!res)exi[id] = false;
	return res;
}
int mostfar(int s) {
	fill(used, used + n, false);
	queue<int> q; used[s] = true; q.push(s);
	int res = s;
	while (!q.empty()) {
		int x = q.front(); q.pop(); res = x;
		rep(i,G[x].size()) {
			int to = G[x][i];
			if (used[to])continue;
			if (!exi[to])continue;
			used[to] = true; q.push(to);
		}
	}
	return res;
}
vector<int> road;
bool ontheroad[1 << 17];
int l, r;
int d[1 << 17];
void searchroad() {
	fill(used, used + n, false);
	queue<int> q; used[l] = true; q.push(l);
	int cnt = 1;
	while (!q.empty()) {
		int len = q.size();
		rep(j, len) {
			int x = q.front(); q.pop();
			d[x] = cnt;
			rep(i, G[x].size()) {
				int to = G[x][i];
				if (used[to])continue;
				if (!exi[to])continue;
				used[to] = true; q.push(to);
			}
		}
		cnt++;
	}
	int cur = r; road.push_back(r); ontheroad[r] = true;
	while (cur != l) {
		rep(i, G[cur].size()) {
			int to = G[cur][i];
			if (d[to] == d[cur] - 1) {
				road.push_back(to);
				ontheroad[to] = true;
				cur = to;
				break;
			}
		}
	}
	
}
int dfs(int id) {
	int res = 0;
	int needed = (c[id] == 'W');
	needed ^= 1;
	used[id] = true;
	rep(j, G[id].size()) {
		int to = G[id][j];
		if (used[to])continue;
		if (!exi[to])continue;
		res += 2 + dfs(to); needed ^= 1;
	}
	if (needed)res++;
	return res;
}
int calc() {
	fill(used, used + n, false);
	int res = 1;
	rep(i, road.size()) {
		int x = road[i]; used[x] = true;
		int needed = (c[x] == 'W');
		needed ^= 1;
		rep(j, G[x].size()) {
			int to = G[x][j];
			if (!exi[to])continue;
			if (ontheroad[to])continue;
			res += 2 + dfs(to); needed ^= 1;
		}
		if (needed)res++;
	}
	res += road.size() - 1;
	return res;
}
int main() {
	int num = 0;
	cin >> n; fill(exi, exi + n, true);
	rep(i, n - 1) {
		int a, b; cin >> a >> b; a--; b--;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	cin >> c;
	root = -1;
	rep(i, n) {
		if (c[i] == 'W') {
			root = i; num++;
		}
	}
	if (root < 0) {
		cout << 0 << endl; return 0;
	}
	else if (num == 1) {
		cout << 1 << endl; return 0;
	}
	maketree(root);
	l = mostfar(root), r = mostfar(l);
	searchroad();
	cout << calc() << endl;

	//stop
	return 0;
}

Submission Info

Judge Result