pku1273 Drainage Ditches

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

网络流，Dinic

#include <stdio.h>
#include <string.h>
#include <queue>

using namespace std;

const int inf = 1<<30;
const int maxn = 202, maxm = 202;

struct Edge
{
    int v, f, nxt;
};

int n, src, sink;
int g[maxn + 10];
int nume;
Edge e[maxm*2 + 10];

void addedge(int u, int v, int c)
{
    e[++nume].v = v;
    e[nume].f = c;
    e[nume].nxt = g[u];
    g[u] = nume;
    e[++nume].v = u;
    e[nume].nxt = g[v];
    g[v] = nume;
}


queue<int> que;
bool vis[maxn + 10];
int dist[maxn + 10];

void bfs()
{
    memset(dist, 0, sizeof(dist));
    while(!que.empty())
    {
        que.pop();
    }
    vis[src] = true;
    que.push(src);
    while(!que.empty())
    {
        int u = que.front();
        que.pop();
        for(int i=g[u]; i; i=e[i].nxt)
        {
            if(e[i].f && !vis[e[i].v])
            {
                que.push(e[i].v);
                dist[e[i].v] = dist[u] + 1;
                vis[e[i].v] = true;
            }
        }
    } 
}

int dfs(int u, int delta)
{
    if(u == sink)
    {
        return delta;
    } 
    else
    {
        int ret = 0;
        for(int i=g[u]; delta && i; i=e[i].nxt)
        {
            if(e[i].f && dist[e[i].v] == dist[u] + 1)
            {
                int dd = dfs(e[i].v, min(e[i].f, delta));
                e[i].f -= dd;
                e[i ^ 1].f += dd;
                delta -= dd;
                ret += dd;
            }
        }
        return ret;
    }
}

int maxflow()
{
    int ret = 0;
    while(true)
    {
        memset(vis, 0, sizeof(vis));
        bfs();
        if(!vis[sink])
        {
            return ret;
        }
        ret += dfs(src, inf);
    } 
}


int main()
{
    int n, m;
    int i, x, y, z;
    while(~scanf("%d%d", &m, &n))
    {
        memset(g, 0, sizeof(g));
        nume = 1;
        src = 1;
        sink = n;
        for(i=1; i<=m; i++)
        {
            scanf("%d%d%d", &x, &y, &z);
            addedge(x, y, z);
        }
        x = maxflow();
        printf("%d
", x);
    }
    return 0;
}