mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
91 lines
2.1 KiB
C++
91 lines
2.1 KiB
C++
#include <iostream>
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#include <cstdio>
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#include <cstring>
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#include <cassert>
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#include <queue>
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#include <vector>
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#include <map>
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#include <set>
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#include <cmath>
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#include <algorithm>
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using namespace std;
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#define rep(i,a,b) for(int i=(a);i<(int)(b);++i)
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#define rrep(i,b,a) for(int i=(b);i>=(int)(a);--i)
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#define eps 1e-8
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#define clr(a,x) memset(a,x,sizeof(a))
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#define LL long long
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const int maxn = 10000+5;
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int p[maxn];
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int find(int x)
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{
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if (x == p[x]) return x;
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return p[x] = find(p[x]);
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}
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int u[maxn*4],v[maxn*4],c[maxn*4];
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int id[maxn],tot;
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double A[500][500];
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int N,M,S,T;
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void input()
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{
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scanf("%d%d%d%d",&N,&M,&S,&T);
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rep(i,0,M) scanf("%d%d%d",u+i,v+i,c+i);
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}
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void gauss(int n)
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{
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int i , j , k , r;
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for(i=0; i < n; ++i) {
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r = i;
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for(j = i+1; j <= n; ++j)
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if (fabs(A[j][i]) > fabs(A[r][i])) r = j;
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if (r != i) for(j = 0; j <= n; ++j) swap(A[r][j],A[i][j]);
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for(j = i+1; j <= n; ++j) A[i][j] /= A[i][i];
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A[i][i] = 1.0;
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for(k = 0; k < n; ++k) {
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if (fabs(A[k][i]) < eps || i == k) continue;
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double f = A[k][i];
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for(j = 0; j <= n; ++j) A[k][j] -= f * A[i][j];
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}
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}
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}
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void solve()
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{
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rep(i,1,N+1) p[i] = i;
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rep(i,0,M) if (c[i] == 0)
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p[find(u[i])] = find(p[v[i]]);
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if (find(S) == find(T)) {
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printf("0.000000\n");
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return;
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}
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tot = 0;
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rep(i,1,N+1)
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if (find(i) == i) id[i] = tot++;
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rep(i,1,N+1)
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id[i] = id[find(i)];
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rep(i,0,tot) p[i] = i;
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rep(i,0,M) p[find(u[i])] = find(v[i]);
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if (find(S) != find(T)) {
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puts("inf");
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return;
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}
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clr(A,0);
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rep(i,0,M) {
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if (id[u[i]] == id[v[i]]) continue;
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int x = id[u[i]] , y = id[v[i]];
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++A[x][x]; --A[x][y];
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++A[y][y]; --A[y][x];
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}
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S = id[S]; T = id[T];
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A[S][tot] = 1.0; A[T][tot] = -1.0;
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A[tot-1][S]++;
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gauss(tot);
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printf("%.6lf\n",-A[T][tot] + A[S][tot] + eps);
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}
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int main()
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{
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int T; cin >> T;
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while (T--) {
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input();
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solve();
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}
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}
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