[정올] 3230 / [백준] 15971 / 두 로봇

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

typedef pair<int, int> p;
vector<p> g[101010];

int dist[101010];
int maxi[101010];
int chk[101010];

void dfs(int v, int d, int m){
	dist[v] = d;
	maxi[v] = m;
	chk[v] = 1;
	for(auto i : g[v]){
		if(!chk[i.first]) dfs(i.first, d + i.second, max(m, i.second));
	}
}

int main(){
	int n, a, b; cin >> n >> a >> b;
	for(int i=0; i<n-1; i++){
		int s, e, x; cin >> s >> e >> x;
		g[s].push_back({e, x});
		g[e].push_back({s, x});
	}
	if(a == b){
		cout << "0"; return 0;
	}
	dfs(a, 0, 0);
	cout << dist[b] - maxi[b];
}