# 【BZOJ1050】[HAOI2006]旅行

bzoj

## 题解

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <vector>
using namespace std;

const int MAX_N = 505;
const int MAX_M = 5005;
int N, M, S, T, fa[MAX_N];
int getf(int x) { return (fa[x] == x) ? x : (fa[x] = getf(fa[x])); }
bool same(int x, int y) { return getf(x) == getf(y); }
void unite(int x, int y) { fa[getf(x)] = getf(y); }
void clear() { for (int i = 1; i <= N; i++) fa[i] = i; }
struct Edge { int u, v, w; } e[MAX_M];
bool operator < (const Edge &a, const Edge &b) { return a.w < b.w; }
double ans = 1e9;
int ansl, ansr;
int main () {
scanf("%d%d", &N, &M);
for (int i = 1; i <= M; i++) scanf("%d%d%d", &e[i].u, &e[i].v, &e[i].w);
scanf("%d%d", &S, &T);
sort(&e[1], &e[M + 1]);
for (int i = 1; i <= M; i++) {
clear(); int j;
for (j = i; j <= M; j++) {
int u = e[j].u, v = e[j].v;
if (!same(u, v)) unite(u, v);
if (same(S, T)) break;
}
if ((ans > 1.0 * e[j].w / e[i].w) && same(S, T))
ans = 1.0 * e[j].w / e[i].w, ansl = e[i].w, ansr = e[j].w;
}
if (ans == 1e9) puts("IMPOSSIBLE");
else {
int d = __gcd(ansl, ansr);
ansl /= d, ansr /= d;
if (ansl == 1) printf("%d\n", ansr);
else printf("%d/%d\n", ansr, ansl);
}
return 0;
}

posted @ 2018-12-26 14:45  heyujun  阅读(78)  评论(0编辑  收藏