POJ 1273

思路：最大流算法，基于FF方法:

1.Dinic:

/*************************************************************************
    > File Name:        Dith.cpp
    > Author:         wangzhili
    > Mail:           wangstdio.h@gmail.com
    > Created Time:   2014年03月07日 星期五 10时47分22秒
 ************************************************************************/

#include<iostream>
#include<queue>
#include<cstring>
#include<cstdio>
#define MAX 205
using namespace std;
int res[MAX][MAX], level[MAX], N, M;
queue<int>q;
bool bfs(int s)
{
    memset(level, -1, sizeof(level));
    while(!q.empty()) q.pop();
    level[s] = 0;
    q.push(s);
    while(!q.empty())
    {
        int p = q.front();
        q.pop();
        for(int i = 1;i <= M;i ++)
        {
            if(level[i] == -1 && res[p][i] > 0)
            {
                level[i] = level[p] + 1;
                q.push(i);
            }
        }
    }
    if(level[M] >= 0)
        return true;
    return false;
}

int Dinic(int s, int sum)
{
    if(s == M)
        return sum;
    int os = sum;
    for(int i = 1;i <= M;i ++)
    {
        if(level[i] == level[s] + 1 && res[s][i] > 0)
        {
            int temp = Dinic(i, min(sum, res[s][i]));
            res[s][i] -= temp;
            res[i][s] += temp;
            sum -= temp;
        }
    }
    return os - sum;
}

int main(int argc, char const *argv[]) 
{
    int flow, u, v, w;
   // freopen("in.c", "r", stdin);
    while(cin >> N >> M)
    {
        flow = 0;
        memset(res, 0, sizeof(res));
        while(N--)
        {
            cin >> u >> v >> w;
            res[u][v] += w;
        }
        while(bfs(1))
            flow += Dinic(1, 1 << 30);
        cout << flow << endl;
    }
    return 0;
}

2.EK：

/*************************************************************************
    > File Name:        EK.cpp
    > Author:         wangzhili
    > Mail:           wangstdio.h@gmail.com
    > Created Time:   2014年03月07日 星期五 11时08分35秒
 ************************************************************************/

#include<iostream>
#include<queue>
#include<cstring>
#include<cstdio>
#define MAX 205
using namespace std;
int res[MAX][MAX], vis[MAX], pre[MAX], N, M;
queue<int>q;
bool bfs(int s, int t)
{
    memset(vis, 0, sizeof(vis));
    memset(pre, -1, sizeof(pre));
    while(!q.empty()) q.pop();
    vis[s] = 1;
    q.push(s);
    while(!q.empty())
    {
        int p = q.front();
        q.pop();
        for(int i = 1;i <= M;i ++)
        {
            if(!vis[i] && res[p][i] > 0)
            {
                vis[i] = 1;
                pre[i] = p;
                if(i == t)
                    return true;
                q.push(i);
            }
        }
    }
    return false;
}

int EK(int s, int t)
{
    int d, u;
    d = 1 << 30;
    u = t;
    while(pre[u] != -1)
    {
        d = min(d, res[pre[u]][u]);
        u = pre[u];
    }
    u = t;
    while(pre[u] != -1)
    {
        res[pre[u]][u] -= d;
        res[u][pre[u]] += d;
        u = pre[u];
    }
    return d;
}
int main(int argc, char const *argv[]) 
{
    int u, v, w, flow;
   // freopen("in.c", "r", stdin);
    while(cin >> N >> M)
    {
        flow = 0;
        memset(res, 0, sizeof(res));
        while(N--)
        {
            cin >> u >> v >> w;
            res[u][v] += w;
        }
        while(bfs(1, M))
            flow += EK(1, M);
        cout << flow << endl;
    }
    return 0;
}