HDU 3376 最小费用最大流

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <algorithm>
#include <iostream>
#include <string>
#include <set>
#define X first
#define Y second
#define sqr(x) (x)*(x)
#pragma comment(linker,"/STACK:102400000,102400000")
using namespace std;
const double PI = acos(-1.0);
map<int, int>::iterator it;
typedef long long LL ;
template<typename T> void checkmin(T &x, T y) {x = min(x, y);}
template<typename T> void checkmax(T &x, T y) {x = max(x, y);}

const LL inf = 1LL << 56;
const int N = 360006 * 2;
const int M = N * 5;
struct Edge {
    int st, en,   next;
    LL flow, cost, cap;
} E[M];
int head[N] , nedge , now[N], node;
int src, dest, pre[N];
LL dis[N];
queue<int> q;
bool vs[N];

void add_edge(int st, int en, LL cap, LL cost) {
    E[nedge].st = st;
    E[nedge].en = en;
    E[nedge].cap = cap;
    E[nedge].flow = 0;
    E[nedge].cost = cost;
    E[nedge].next = head[st];
    head[st] = nedge++;

    E[nedge].st = en;
    E[nedge].en = st;
    E[nedge].cap = 0;
    E[nedge].flow = 0;
    E[nedge].cost = -cost;
    E[nedge].next = head[en];
    head[en] = nedge++;
}

bool SPFA() {
    for(int i = 0; i < node; i++)
        dis[i] = inf;
    memset(vs, 0, sizeof(vs));
    memset(now, -1, sizeof(now));
    while(!q.empty()) q.pop();
    q.push(src); dis[src] = 0; vs[src] = 1;
    while(!q.empty()) {
        int u = q.front(); q.pop(); vs[u] = 0;
        for(int i = head[u], v; i != -1; i = E[i].next)
            if(E[i].cap - E[i].flow > 0 && dis[v=E[i].en] > dis[u] + E[i].cost) {
                dis[v] = dis[u] + E[i].cost;
                now[v] = i;
                if(!vs[v]) {
                    vs[v] = 1;
                    q.push(v);
                }
            }
    }
    if(dis[dest] != inf) return true;
    else return false;
}

void MCMF(LL &flow, LL &cost) {
    cost = 0, flow = 0;
    while(SPFA()) {
        LL fw = inf;
        for(int u = dest; u != src; u = E[now[u]].st)
            if(fw > E[now[u]].cap - E[now[u]].flow)
                fw = E[now[u]].cap - E[now[u]].flow;
        for(int u = dest; u != src; u = E[now[u]].st) {
            E[now[u]].flow += fw;
            E[now[u] ^ 1].flow -= fw;
        }
        flow += fw;
        cost += fw * dis[dest];
    }
}

void init(int _node, int _src, int _dest) {
    nedge = 0;
    node = _node;
    src = _src;
    dest = _dest;
    for(int i = 0; i < node; i++)head[i] = -1;
}

const int SN = 606;
int a[SN][SN];

int main() {
    int n;
    while(~scanf("%d", &n)) {
        int m = n * n;
        init(2 * m + 2 , 0, 2 * m - 1);
        for(int i = 0; i < n; ++i) {
            for(int j = 0; j < n; ++j) {
                scanf("%d", &a[i][j]);
                int id = i * n + j;
                int cap = 1;
                if(i == 0 && j == 0 || i == n - 1 && j == n - 1)cap = 2;
                add_edge(id, id + m, cap, -a[i][j]);
                if(i < n - 1)add_edge(id + m, id + n , 1, 0);
                if(j < n - 1)add_edge(id + m, id + 1, 1, 0);
            }
        }

        LL res = 0, cost = 0, flow = 0;
        MCMF(flow, cost);
        res += -(cost+a[0][0]+a[n-1][n-1]);
        //printf("cost = %I64d flow = %I64d\n", cost, flow);
        printf("%I64d\n", res);
    }
    return 0;
}