【BZOJ1001】狼抓兔子

题面

bzoj

题解

懒得平面图转对偶图了，直接最小割板子加优化。

#include <iostream> 
#include <cstdio> 
#include <cstdlib> 
#include <cstring> 
#include <cmath> 
#include <algorithm>
#include <queue>
#include <climits> 
using namespace std; 
inline int gi() {
    register int data = 0, w = 1;
    register char ch = 0;
    while (!isdigit(ch) && ch != '-') ch = getchar(); 
    if (ch == '-') w = -1, ch = getchar();
    while (isdigit(ch)) data = 10 * data + ch - '0', ch = getchar();
    return w * data; 
}
const int MAX_N = 1005; 
struct Graph { int to, cap, rev, next; } e[MAX_N * MAX_N * 6]; int fir[MAX_N * MAX_N], e_cnt = 0; 
void clearGraph() { memset(fir, -1, sizeof(fir)); e_cnt = 0; } 
void Add_Edge(int u, int v, int c) { 
    e[e_cnt] = (Graph){v, c, e_cnt + 1, fir[u]}; fir[u] = e_cnt++; 
    e[e_cnt] = (Graph){u, c, e_cnt - 1, fir[v]}; fir[v] = e_cnt++; 
} 
queue<int> que; 
int V, iter[MAX_N * MAX_N], level[MAX_N * MAX_N]; 
void bfs(int s) { 
    fill(&level[1], &level[V + 1], -1); 
    while (!que.empty()) que.pop(); 
    level[s] = 0; que.push(s); 
    while (!que.empty()) { 
        int x = que.front(); que.pop(); 
        for (int i = fir[x]; ~i; i = e[i].next) { 
            int v = e[i].to; 
            if (level[v] < 0 && e[i].cap > 0) { 
                level[v] = level[x] + 1; 
                que.push(v); 
            } 
        } 
    } 
} 
int dfs(int x, int t, int f) { 
    if (x == t) return f; 
    for (int &i = iter[x]; ~i; i = e[i].next) { 
        int v = e[i].to; 
        if (e[i].cap > 0 && level[v] > level[x]) { 
            int d = dfs(v, t, min(f, e[i].cap)); 
            if (d) { 
                e[i].cap -= d; 
                e[e[i].rev].cap += d; 
                return d; 
            } 
        } 
    } 
    level[x] = -1; 
    return 0; 
} 
int max_flow(int s, int t) { 
    int flow = 0; 
    for (;;) { 
        for (int i = 1; i <= V; i++) iter[i] = fir[i]; 
        bfs(s); 
        if (level[t] == -1) return flow; 
        int f = 0; 
        while (f = dfs(s, t, INT_MAX)) flow += f; 
    } 
} 
int N, M, S, T, id[MAX_N][MAX_N], cnt; 
int main () { 
#ifndef ONLINE_JUDGE 
    freopen("cpp.in", "r", stdin); 
#endif
    clearGraph(); 
    N = gi(), M = gi(); 
    int cnt = 0; S = 1;
    for (int i = 1; i <= N; i++)
        for (int j = 1; j <= M; j++)
            id[i][j] = ++cnt;
    T = id[N][M]; V = cnt; 
    for (int i = 1; i <= N; i++)
        for (int j = 1; j < M; j++) 
            Add_Edge(id[i][j], id[i][j + 1], gi()); 
    for (int i = 1; i < N; i++)
        for (int j = 1; j <= M; j++)
            Add_Edge(id[i][j], id[i + 1][j], gi());
    for (int i = 1; i < N; i++)
        for (int j = 1; j < M; j++)
            Add_Edge(id[i][j], id[i + 1][j + 1], gi()); 
    printf("%d\n", max_flow(S, T)); 
    return 0; 
}