POJ 1273

来源：互联网发布：java内存泄露例子编辑：程序博客网时间：2024/05/16 10:58

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 205using 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 205using 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;}

0 0