POJ 3422 Kaka's Matrix Travels 费用流

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<queue>
using namespace std;
#define maxn 5010
#define maxm 10030
#define inf 1000000000

int min(int a, int b)
{
    return a < b ? a : b;
}
struct E
{
    int u, v, c, w, next;
}edge[maxm<<3];

int head[maxn], tot;
int n, m, k;
int S, T;
void init()
{
    tot = 0;
    memset(head, -1, sizeof(head));
}

void add(int s, int t, int c, int w)
{
    edge[tot].u = s;
    edge[tot].v = t;
    edge[tot].c = c;
    edge[tot].w = w;
    edge[tot].next = head[s];
    head[s] = tot++;
    
    edge[tot].u = t;
    edge[tot].v = s;
    edge[tot].c = 0;
    edge[tot].w = -w;
    edge[tot].next = head[t];
    head[t] = tot++;
}

bool vis[maxn];
int pre[maxn];
int dis[maxn];
bool spfa(int s, int t, int n)
{
    int i, u, v;
    for(i = 0; i <= n; i++)
        vis[i] = 0, pre[i] = -1, dis[i] = -inf;
    queue<int> q;
    q.push(s); vis[s] = 1; dis[s] = 0;
    while(!q.empty())
    {
        u = q.front(); q.pop(); vis[u] = 0;
        for(i = head[u]; i != -1; i = edge[i].next)
        {
            v = edge[i].v;
            if(edge[i].c && dis[v] < dis[u] + edge[i].w)
            {
                dis[v] = dis[u] + edge[i].w;
                pre[v] = i; 
                if(!vis[v])
                {
                    vis[v] = 1;
                    q.push(v);
                }
            }
        }
    
    }
    if(dis[t] == -inf) return 0;
    return 1;
}

int mfmw(int s, int t, int n) 
{
    int i, maxf = 0, minw = 0, aug;
    while(spfa(s, t, n))
    {
        aug = inf;
        for(i = pre[t]; i != -1; i = pre[edge[i].u])
            aug = min(aug, edge[i].c);
        for(i = pre[t]; i != -1; i = pre[edge[i].u])
        {
            edge[i].c -= aug;
            edge[i^1].c += aug;
        }
        maxf += aug;
        minw += dis[t] * aug;
    }
    return minw;
}

int main()
{
    int i, j;
    int x, y, z;
    while( ~scanf("%d%d", &n, &k))
    {
        init();
        S = 0; T = 2*n*n+1;
        add(S, 1, k, 0);
        add(n*n*2, T, k, 0);
        for(i = 1; i <= n; i++)
            for(j = 1; j <= n; j++)
            {
                scanf("%d", &z);
                x = (i-1)*n+j;
                add(x, x+n*n, 1, z);
                add(x, x+n*n, inf, 0);
                if(i < n) add(x+n*n, x+n, inf, 0);
                if(j < n) add(x+n*n, x+1, inf, 0);
                
            }
        printf("%d\n", mfmw(S, T, T+1));
    }
    return 0;
}