POJ 1273 Drainage Ditches 最大流

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http://poj.org/problem?id=1273
题目大意：
给你N条路径（有重边），和M个点，求以1为源点，M为汇点的最大流。
思路：
第一题最大流问题，直接用Edmonds-Karp算法即可

#include<cstdio>#include<cstring>#include<queue>#include<algorithm>using namespace std;const int MAXN = 1<<8;int map[MAXN][MAXN];int flow[MAXN];int pre[MAXN];int n, m;int bfs(int s,int t){memset(pre, -1, sizeof(pre));queue<int> q;q.push(s);pre[s] = 0;flow[s] = 0x3ffffff;while (!q.empty()){int cur = q.front();q.pop();for (int i = 1; i <= m; i++) {if (map[cur][i] > 0 && pre[i] == -1){flow[i] = min(flow[cur],map[cur][i]);pre[i] = cur;q.push(i);}}}return pre[t] == -1 ? -1 : flow[t];}int maxFlow(int s,int t){int ans = 0;int curFlow=0;while ((curFlow=bfs(s,t))  !=-1){int cur = t;while (cur != s){map[pre[cur]][cur] -= curFlow;map[cur][pre[cur]] += curFlow;cur = pre[cur];}ans += curFlow;}return ans;}int main(){while (~scanf("%d%d", &n, &m)){memset(map, 0, sizeof(map));for (int i = 0; i < n; i++){int from, to, val;scanf("%d%d%d", &from, &to, &val);map[from][to] += val;}printf("%d\n", maxFlow(1,m));}}

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