hdu 1532 Drainage Ditches(最大流)

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题目：

链接：点击打开链接

题意：

求最大流速。

思路：

Edmond_karp就行。

代码：

#include <iostream>#include <cstdio>#include <cstring>#include <queue>using namespace std;#define INF 100000000const int N = 220;int cap[N][N],flow[N][N];int a[N];int n,m;int s,e,c;void edmonds_karp(int s,int t){    queue<int> q;    memset(flow,0,sizeof(flow));    int f = 0;    int p[N];    for(;;)    {        memset(a,0,sizeof(a));        a[s] = INF;        q.push(s);        while(!q.empty())        {            int u = q.front();            q.pop();            for(int v=1; v<=n; v++)            {                if(!a[v] && cap[u][v] > flow[u][v])                {                    p[v] = u;                    q.push(v);                    a[v] = a[u] < cap[u][v] - flow[u][v] ? a[u] : cap[u][v] - flow[u][v];                }            }        }        if(a[t] == 0)            break;        for(int u=t; u!=s; u=p[u])        {            flow[p[u]][u] += a[t];            flow[u][p[u]] += a[t];        }        f += a[t];    }    printf("%d\n",f);}int main(){    //freopen("input.txt","r",stdin);    while(scanf("%d%d",&n,&m) != EOF)    {        memset(cap,0,sizeof(cap));        for(int i=0; i<n; i++)        {            scanf("%d%d%d",&s,&e,&c);            cap[s][e] += c;        }        edmonds_karp(1,m);    }    return 0;}

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收获：

------>增广路算法，Edmond_karp模板：

queue<int> q;    memset(flow,0,sizeof(flow));    int f = 0;    int p[N];    for(;;)    {        memset(a,0,sizeof(a));        a[s] = INF;        q.push(s);        while(!q.empty())        {            int u = q.front();            q.pop();            for(int v=1; v<=n; v++)            {                if(!a[v] && cap[u][v] > flow[u][v])                {                    p[v] = u;                    q.push(v);                    a[v] = a[u] < cap[u][v] - flow[u][v] ? a[u] : cap[u][v] - flow[u][v];                }            }        }        if(a[t] == 0)            break;        for(int u=t; u!=s; u=p[u])        {            flow[p[u]][u] += a[t];            flow[u][p[u]] += a[t];        }        f += a[t];    }

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战斗，从不退缩；奋斗，永不停歇~~~~~~~~~~~~~

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