题目链接

最大流

如果是单向边，那么反向弧的容量和流量都设置为0，否则容量和流量都和正向边一样。

有弧优化可以不用炸点优化

 
#include <iostream>
#include <cstdio>
#include <cstring>
#include <map>
#include <vector>
#include <cmath>
#include <algorithm>
#include <queue>
#include <stack>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;

const int Maxn = 1e6+10;
const int INF = 0x3f3f3f3f;
const long long LINF = 1e18;

struct Edge {
    int v, cap, flow, next;
} edge[Maxn*6];

int h[Maxn], edge_cnt;
int indx[Maxn], deep[Maxn], qu[Maxn];

void add(int u, int v, int c) {
    edge[edge_cnt].v = v;
    edge[edge_cnt].cap = c;
    edge[edge_cnt].flow = 0;
    edge[edge_cnt].next = h[u];
    h[u] = edge_cnt++;

    edge[edge_cnt].v = u;
    edge[edge_cnt].cap = c;
    edge[edge_cnt].flow = 0;
    edge[edge_cnt].next = h[v];
    h[v] = edge_cnt++;
}

bool bfs(int s, int t) {
    int head = 0, tail = 0;
    memset(deep, 0, sizeof(deep));
    deep[s] = 1; qu[tail++] = s;
    while(head < tail) {
        int u = qu[head++];
        for(int i = h[u]; i != -2; i = edge[i].next) {
            Edge &e = edge[i];
            if(deep[e.v] == 0 && e.cap-e.flow > 0) {
                deep[e.v] = deep[u]+1;
                qu[tail++] = e.v;
            }
        }
    }
    if(deep[t] > 0) return true;
    else return false;
}

int dfs(int cur, int t, int a) {
    if(cur == t || a == 0) return a;
    int flow = 0, f;
    if(indx[cur] == -1) indx[cur] = h[cur];
    for(int &i = indx[cur]; i != -2; i = edge[i].next) {
        Edge &e = edge[i];
        if(deep[e.v] == deep[cur]+1) {
            f = dfs(e.v, t, min(a, e.cap-e.flow));
            if(f > 0) {
                e.flow += f;
                edge[i^1].flow -= f;
                flow += f;
                a -= f;
                if(a == 0) break;
            }
        }
    }
  //  if(flow == 0) deep[cur] = -2; // 有弧优化，炸点优化可以不要
    return flow;
}

void dinic(int s, int t) {
    int ans = 0;
    while(bfs(s, t)) {
        memset(indx, -1, sizeof(indx));
        ans += dfs(s, t, INF);
    }
    printf("%d\n", ans);
    return;
}

int main(void)
{
	int N, M, c;
	scanf("%d%d", &N, &M);
	for(int i = 0; i < Maxn; ++i) h[i] = -2;
	edge_cnt = 0;
	for(int i = 0; i < N; ++i) {
        for(int j = 0; j < M-1; ++j) {
            scanf("%d", &c);
            add(i*M+j, i*M+j+1, c);
        }
	}
	for(int i = 0; i < N-1; ++i) {
        for(int j = 0; j < M; ++j) {
            scanf("%d", &c);
            add(i*M+j, (i+1)*M+j, c);
        }
	}
	for(int i = 0; i < N-1; ++i) {
        for(int j = 0; j < M-1; ++j) {
            scanf("%d", &c);
            add(i*M+j, (i+1)*M+j+1, c);
        }
	}
	dinic(0, N*M-1);
	return 0;
}