题目：http://vjudge.net/problem/UVA-11183
题意：以0为根构建一个最小树形图，求最小花费
思路：裸题，没什么好说的
#include <iostream> #include <cstdio> #include <cstring> #include <string> #include <algorithm> #include <cmath> #include <queue> #include <map> using namespace std; const int N = 1010, INF = 0x3f3f3f3f; struct edge { int v, u, cost; }g[N*40]; int n, m, cas; int in[N], pre[N], id[N], vis[N]; int ma(int s, int n, int m) { int res = 0; while(true) { for(int i = 0; i < n; i++) in[i] = INF; for(int i = 0; i < m; i++) { int v = g[i].v, u = g[i].u; if(v != u && g[i].cost < in[u]) in[u] = g[i].cost, pre[u] = v; } for(int i = 0; i < n; i++) { if(i == s) continue; if(in[i] == INF) return -1; } int num = 0; memset(id, -1, sizeof id); memset(vis, -1, sizeof vis); in[s] = 0; for(int i = 0; i < n; i++) { res += in[i]; int v = i; while(vis[v] != i && id[v] == -1 && v != s) vis[v] = i, v = pre[v]; if(v != s && id[v] == -1) { for(int j = pre[v]; j != v; j = pre[j]) id[j] = num; id[v] = num++; } } if(num == 0) break; for(int i = 0; i < n; i++) if(id[i] == -1) id[i] = num++; for(int i = 0; i < m; i++) { int v = g[i].v, u = g[i].u; g[i].v = id[v], g[i].u = id[u]; if(id[v] != id[u]) g[i].cost -= in[u]; } n = num, s = id[s]; } return res; } int main() { int t; scanf("%d", &t); while(t--) { scanf("%d%d", &n, &m); for(int i = 0; i < m; i++) scanf("%d%d%d", &g[i].v, &g[i].u, &g[i].cost); int res = ma(0, n, m); if(res != -1) printf("Case #%d: %d\n", ++cas, res); else printf("Case #%d: Possums!\n", ++cas); } return 0; }