题目链接:
PREV-9 大臣的旅费
思路:
根据题意,该国路线图是一颗树,则题意是求此树的直径;
用两次dfs/bfs即可求得一棵树的直径;
代码:
#include<bits/stdc++.h>
using namespace std;
struct edge { int to, cost; };
vector<vector<edge> > G;
vector<bool> vst;
int n;
int ans, dis;
void dfs(int u, int d) {
vst[u] = true;
if(d > dis) ans = u, dis = d;
for(int i = 0; i < G[u].size(); i++) {
int son = G[u][i].to;
if(!vst[son]) dfs(son, G[u][i].cost + d);
}
vst[u] = false;
}
int find(int u) { ans = dis = 0; dfs(u, 0); return ans; }
int main() {
#ifdef MyTest
freopen("Sakura.txt", "r", stdin);
#endif
scanf("%d", &n);
G.resize(n + 5), vst.resize(n + 5);
for(int i = 1; i < n; i++) {
int p, q, d;
scanf("%d %d %d", &p, &q, &d);
G[p].push_back(edge{q, d});
G[q].push_back(edge{p, d});
}
int x = find(1), y = find(x);
printf("%d", dis * (dis + 1) / 2 + 10 * dis);
return 0;
}