[POJ 1273] Drainage Ditches

[题目链接]

         http://poj.org/problem?id=1273

[算法]

         最大流

[代码]

        

#include <algorithm>  
#include <bitset>  
#include <cctype>  
#include <cerrno>  
#include <clocale>  
#include <cmath>  
#include <complex>  
#include <cstdio>  
#include <cstdlib>  
#include <cstring>  
#include <ctime>  
#include <deque>  
#include <exception>  
#include <fstream>  
#include <functional>  
#include <limits>  
#include <list>  
#include <map>  
#include <iomanip>  
#include <ios>  
#include <iosfwd>  
#include <iostream>  
#include <istream>  
#include <ostream>  
#include <queue>  
#include <set>  
#include <sstream>  
#include <stdexcept>  
#include <streambuf>  
#include <string>  
#include <utility>  
#include <vector>  
#include <cwchar>  
#include <cwctype>  
#include <stack>  
#include <limits.h>
using namespace std;
#define MAXN 210
const int inf = 2e9;

struct edge
{
        int to,w,nxt;
} e[MAXN << 1];

int i,tot,n,m,u,v,w,maxflow,flow;
int head[MAXN],depth[MAXN];

inline void addedge(int u,int v,int w)
{
        tot++;
        e[tot] = (edge){v,w,head[u]};
        head[u] = tot;
        tot++;
        e[tot] = (edge){u,0,head[v]};
        head[v] = tot;
}
inline bool bfs()
{
        int i,l,r,u,v,w;
        static int q[MAXN];
        q[l = r = 1] = 1;
        memset(depth,0,sizeof(depth));
        depth[1] = 1;
        while (l <= r)
        {
                u = q[l];
                l++;
                for (i = head[u]; i; i = e[i].nxt)
                {
                        v = e[i].to;
                        w = e[i].w;
                        if (w && !depth[v])
                        {
                                depth[v] = depth[u] + 1;
                                if (v == n) return true;
                                q[++r] = v;
                        }
                }
        }
        return false;
}
inline int dinic(int u,int flow)
{
        int i,v,w,rest = flow,k;
        if (u == n) return flow;
        for (i = head[u]; i && rest; i = e[i].nxt)
        {
                v = e[i].to;
                w = e[i].w;
                if (w && depth[v] == depth[u] + 1)
                {
                        k = dinic(v,min(rest,w));
                        if (!k) depth[v] = 0;
                        e[i].w -= k;
                        e[i ^ 1].w += k;
                        rest -= k;
                }
        }        
        return flow - rest;
}

int main() 
{
        
        while (scanf("%d%d",&m,&n) != EOF)
        {
                tot = 1;
                memset(head,0,sizeof(head));
                for (i = 1; i <= m; i++)
                {
                        scanf("%d%d%d",&u,&v,&w);
                        addedge(u,v,w);
                }
                maxflow = 0;
                while (bfs())
                {
                        while (flow = dinic(1,inf)) maxflow += flow;
                }
                printf("%d\n",maxflow);
        }
        
        return 0;
    
}