标签：c   图论   网络流   

Matrix

2
10 3
5 10
3
10 3 3
2 5 3
6 7 10
5
1 2 3 4 5
2 3 4 5 6
3 4 5 6 7
4 5 6 7 8
5 6 7 8 9

28
46
80

和HPU3376一模一样， 但是数据比较弱，果断水了。

具体的解析请看这里 ：HPU3376

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#define INF 0x3f3f3f3f
#define maxn 800000 + 1000
#define maxm 4000000 + 1000
using namespace std;
int n;
int outset;
int inset;
struct node {
    int u, v, cap, flow, cost, next;
};

node edge[maxm];
int head[maxn], cnt;
int per[maxn];
int dist[maxn], vis[maxn];
int map[660][660];

void init(){
    cnt = 0;
    memset(head, -1, sizeof(head));
}

void add(int u, int v, int w, int c){
    node E1 = {u, v, w, 0, c, head[u]};
    edge[cnt] = E1;
    head[u] = cnt++;
    node E2 = {v, u, 0, 0, -c, head[v]};
    edge[cnt] = E2;
    head[v] = cnt++;
}

int change(int x, int y){
    return (x - 1) * n + y;
}

void getmap(){
    int t = n * n;
    outset = 0;
    inset = n * n * 2 + 1;
    for(int i = 1; i <= n; ++i){
        for(int j = 1; j <= n; ++j){
            scanf("%d", &map[i][j]);
            if(i == 1 && j == 1 || i == n && j == n)
                add(change(i, j), change(i, j) + t, 2, map[i][j]);
            else
                add(change(i, j), change(i, j) + t, 1, map[i][j]);
            if(i + 1 <= n)
                add(change(i, j) + t, change(i + 1, j), 1, 0);
            if(j + 1 <= n)
                add(change(i, j) + t, change(i, j + 1), 1, 0);
        }
    }
    add(outset, 1, 2, 0);
    add(change(n, n) + t, inset, 2, 0);
}

bool SPFA(int st, int ed){
    queue<int>q;
    for(int i = 0; i <= inset; ++i){
        dist[i] = -INF;
        vis[i] = 0;
        per[i] = -1;
    }
    dist[st] = 0;
    vis[st] = 1;
    q.push(st);
    while(!q.empty()){
        int u = q.front();
        q.pop();
        vis[u] = 0;
        for(int i = head[u]; i != -1; i = edge[i].next){
            node E = edge[i];
            if(dist[E.v] < dist[u] + E.cost && E.cap > E.flow){
                dist[E.v] = dist[u] + E.cost;
                per[E.v] = i;
                if(!vis[E.v]){
                    vis[E.v] = 1;
                    q.push(E.v);
                }
            }
        }
    }
    return per[ed] != -1;
}

void MCMF(int st, int ed, int &cost, int &flow){
    flow = 0;
    cost = 0;
    while(SPFA(st, ed)){
        int mins = INF;
        for(int i = per[ed]; i != -1; i = per[edge[i ^ 1].v]){
            mins = min(mins, edge[i].cap - edge[i].flow);
        }
        for(int i = per[ed]; i != -1; i = per[edge[i ^ 1].v]){
            edge[i].flow += mins;
            edge[i ^ 1].flow -= mins;
            cost += edge[i].cost * mins;
        }
        flow += mins;
    }
}
int main (){
    while(scanf("%d", &n) != EOF){
        init();
        getmap();
        int cost, flow;
        MCMF(outset, inset, cost, flow);
        cost = cost - map[1][1] - map[n][n];
        printf("%d\n", cost);
    }
    return 0;
}

HPU 2686--Matrix【最大费用最大流 && 经典建图】

标签：c   图论   网络流   

原文地址：http://blog.csdn.net/hpuhjh/article/details/48050125