POJ - 1459 Power Network(网络流最大流)

最新推荐文章于 2021-05-13 08:57:11 发布

原创最新推荐文章于 2021-05-13 08:57:11 发布 · 266 阅读

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本文解析了POJ-1459题目，通过将问题转化为最大流问题并使用Dinic算法求解。介绍了具体的实现细节，包括读取输入数据的方法和当前弧优化技巧。

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POJ - 1459

题意：看题看的心累，其实就是所有power station是源点，所有consumer是汇点，然后就是一个最大流问题了~
读入写的有点蠢，其实scanf(" ()") 这种就够啦~
另外，对于单路增广的dinic来说，当前弧优化真的很有必要。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <cmath>
#include <queue>
using namespace std;
const int maxn = 200 + 10, maxe = maxn*maxn;
const int inf = 0x3f3f3f3f;
struct node
{
    int to,next,cap,rev;
    node(){}
    node(int a,int b,int c,int d){to = a; next = b; cap = c; rev = d;}
}edge[maxe << 2];
int num;
int h[maxn],deg[maxn],cur[maxn];
int n,np,nc,m;
int s,t;    //源， 汇
void init()
{
    for(int i = 0; i < maxn; i++)
        h[i] = -1,deg[i]  = 0;
    s = 0, t = n+1;
    num = 0;
}
void add(int u,int v,int cap)
{
    edge[num] = node(v,h[u],cap,num+1); h[u] = num++;
    edge[num] = node(u,h[v],0,num-1);   h[v] = num++;
}
int bfs()
{
    for(int i = 0; i < maxn; i++) deg[i] = -1;
    queue<int> q;
    q.push(0);
    deg[0] = 0;
    while(!q.empty())
    {
        int u = q.front(); q.pop();
        for(int i = h[u] ; ~i ; i = edge[i].next)
        {
            int v = edge[i].to,cap = edge[i].cap;
            if(cap && deg[v] == -1)
            {
                deg[v] = deg[u] + 1;
                q.push(v);
            }
        }
    }
    return deg[t] != -1;
}
int dfs(int u,int f)
{
    if(u == t) return f;
    for(int i = cur[u]; ~i; i = edge[i].next)
    {
        cur[u] = i;
        int v = edge[i].to,cap = edge[i].cap, rev = edge[i].rev;
        if(cap && deg[v] == deg[u] + 1)
        {
            int k = dfs(v,min(f,cap));
            if(k == 0) continue;
            edge[i].cap -= k;
            edge[rev].cap += k;
            return k;
        }
    }
    return 0;
}
void solve()
{
    int flow = 0;
    while(bfs())
    {
        for(int i = 0; i < maxn; i++)
            cur[i] = h[i];
        for(;;)
        {
            int k = dfs(0,inf);
            if(k == 0) break;
            flow += k;
        }
    }
    printf("%d\n",flow);
}
char str[1000];

void readnum(int way)
{
    int v = 0,cap = 0;
    scanf("%s",str); int slen = strlen(str);
    int j;
    for(j = 1; j < slen; j++)
    {
        if(str[j] == ')') break;
        v = v*10 + str[j] - '0';
    }
    j++;
    for(; j < slen; j++)
        cap = cap*10 + str[j] - '0';
    if(way) add(s,v+1,cap);
    else add(v+1,t,cap);
}

void read()
{
    for(int i = 0; i < m; i++)
    {
        int u = 0,v = 0,cap = 0;
        scanf("%s",str);
        int slen = strlen(str);
        int j;
        for(j = 1; j < slen;j++)
        {
            if(str[j] == ',') break;
            u = u*10 + str[j] - '0';
        }
        j++;
        for(; j < slen; j++)
        {
            if(str[j] == ')') break;
            v = v*10 + str[j] - '0';
        }
        j++;
        for(; j < slen; j++)
            cap = cap*10 + str[j] - '0';
       // cout << u << " " << v << " " <<cap << endl;
        add(u+1,v+1,cap);
    }
    for(int i = 0; i < np; i++)
        readnum(1);
    for(int i = 0; i < nc; i++)
        readnum(0);

}
int main()
{
    //freopen("D:\\in.txt","r",stdin);
    int a,b,c;
    while(~scanf("%d",&n))
    {
        init();
        scanf("%d%d%d",&np,&nc,&m);
        read();
        solve();
    }
    return 0;
}