注意这道题是双向边， 然后直接套模板就ok了。
#include<cstdio>
#include<algorithm>
#include<vector>
#include<queue>
#include<cstring>
#define REP(i, a, b) for(int i = (a); i < (b); i++)
using namespace std;const int MAXN = 112;
struct Edge
{int from, to, cap, flow;Edge(int from = 0,int to = 0,int cap = 0,int flow = 0):from(from),to(to),cap(cap),flow(flow){}
};
vector<Edge> edges;
vector<int> g[MAXN];
int h[MAXN], cur[MAXN], s, t, n, m;void AddEdge(int from, int to, int cap)
{edges.push_back(Edge(from, to, cap, 0));edges.push_back(Edge(to, from, 0, 0));g[from].push_back(edges.size() - 2);g[to].push_back(edges.size() - 1);
}bool bfs()
{memset(h, 0, sizeof(h));queue<int> q;q.push(s);h[s] = 1;while(!q.empty()){int x = q.front(); q.pop();REP(i, 0, g[x].size()){Edge& e = edges[g[x][i]];if(e.cap > e.flow && !h[e.to]){h[e.to] = h[x] + 1;q.push(e.to);}}}return h[t];
}int dfs(int x, int a)
{if(x == t || a == 0) return a;int flow = 0, f;for(int i = cur[x]; i < g[x].size(); i++){Edge& e = edges[g[x][i]];if(h[x] + 1 == h[e.to] && (f = dfs(e.to, min(a, e.cap - e.flow))) > 0){e.flow += f;edges[g[x][i] ^ 1].flow -= f;flow += f;if((a -= f) == 0) break;}}return flow;
}int solve()
{int ret = 0;while(bfs()) memset(cur, 0, sizeof(cur)), ret += dfs(s, 1e9);return ret;
}int main()
{int kase = 0;while(~scanf("%d", &n) && n){REP(i, 1, n + 1) g[i].clear();edges.clear();scanf("%d%d%d", &s, &t, &m);while(m--){int u, v, f;scanf("%d%d%d", &u, &v, &f);AddEdge(u, v, f);AddEdge(v, u, f);}printf("Network %d\nThe bandwidth is %d.\n\n", ++kase, solve());}return 0;
}