91 lines
2.1 KiB
C++
91 lines
2.1 KiB
C++
#include <iostream>
|
|
#include <cstdio>
|
|
#include <cstring>
|
|
#include <cassert>
|
|
#include <queue>
|
|
#include <vector>
|
|
#include <map>
|
|
#include <set>
|
|
#include <cmath>
|
|
#include <algorithm>
|
|
using namespace std;
|
|
#define rep(i,a,b) for(int i=(a);i<(int)(b);++i)
|
|
#define rrep(i,b,a) for(int i=(b);i>=(int)(a);--i)
|
|
#define eps 1e-8
|
|
#define clr(a,x) memset(a,x,sizeof(a))
|
|
#define LL long long
|
|
const int maxn = 10000+5;
|
|
int p[maxn];
|
|
int find(int x)
|
|
{
|
|
if (x == p[x]) return x;
|
|
return p[x] = find(p[x]);
|
|
}
|
|
int u[maxn*4],v[maxn*4],c[maxn*4];
|
|
int id[maxn],tot;
|
|
double A[500][500];
|
|
int N,M,S,T;
|
|
void input()
|
|
{
|
|
scanf("%d%d%d%d",&N,&M,&S,&T);
|
|
rep(i,0,M) scanf("%d%d%d",u+i,v+i,c+i);
|
|
}
|
|
void gauss(int n)
|
|
{
|
|
int i , j , k , r;
|
|
for(i=0; i < n; ++i) {
|
|
r = i;
|
|
for(j = i+1; j <= n; ++j)
|
|
if (fabs(A[j][i]) > fabs(A[r][i])) r = j;
|
|
if (r != i) for(j = 0; j <= n; ++j) swap(A[r][j],A[i][j]);
|
|
for(j = i+1; j <= n; ++j) A[i][j] /= A[i][i];
|
|
A[i][i] = 1.0;
|
|
for(k = 0; k < n; ++k) {
|
|
if (fabs(A[k][i]) < eps || i == k) continue;
|
|
double f = A[k][i];
|
|
for(j = 0; j <= n; ++j) A[k][j] -= f * A[i][j];
|
|
}
|
|
}
|
|
}
|
|
void solve()
|
|
{
|
|
rep(i,1,N+1) p[i] = i;
|
|
rep(i,0,M) if (c[i] == 0)
|
|
p[find(u[i])] = find(p[v[i]]);
|
|
if (find(S) == find(T)) {
|
|
printf("0.000000\n");
|
|
return;
|
|
}
|
|
tot = 0;
|
|
rep(i,1,N+1)
|
|
if (find(i) == i) id[i] = tot++;
|
|
rep(i,1,N+1)
|
|
id[i] = id[find(i)];
|
|
rep(i,0,tot) p[i] = i;
|
|
rep(i,0,M) p[find(u[i])] = find(v[i]);
|
|
if (find(S) != find(T)) {
|
|
puts("inf");
|
|
return;
|
|
}
|
|
clr(A,0);
|
|
rep(i,0,M) {
|
|
if (id[u[i]] == id[v[i]]) continue;
|
|
int x = id[u[i]] , y = id[v[i]];
|
|
++A[x][x]; --A[x][y];
|
|
++A[y][y]; --A[y][x];
|
|
}
|
|
S = id[S]; T = id[T];
|
|
A[S][tot] = 1.0; A[T][tot] = -1.0;
|
|
A[tot-1][S]++;
|
|
gauss(tot);
|
|
printf("%.6lf\n",-A[T][tot] + A[S][tot] + eps);
|
|
}
|
|
int main()
|
|
{
|
|
int T; cin >> T;
|
|
while (T--) {
|
|
input();
|
|
solve();
|
|
}
|
|
}
|