[luoguP2774] 方格取数问题（最大点权独立集）

  1 #include <queue>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <iostream>
  5 #define INF 1e9
  6 #define N 10010
  7 #define M 50001
  8 #define min(x, y) ((x) < (y) ? (x) : (y))
  9 
 10 int n, m, cnt, sum, s, t, num;
 11 int head[N], to[M], val[M], next[M], dis[N], cur[N];
 12 int map[101][101], dx[4] = {0, 1, -1, 0}, dy[4] = {1, 0, 0, -1};
 13 
 14 inline int read()
 15 {
 16     int x = 0, f = 1;
 17     char ch = getchar();
 18     for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1;
 19     for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘;
 20     return x * f;
 21 }
 22 
 23 inline void add(int x, int y, int z)
 24 {
 25     to[cnt] = y;
 26     val[cnt] = z;
 27     next[cnt] = head[x];
 28     head[x] = cnt++;
 29 }
 30 
 31 inline bool bfs()
 32 {
 33     int i, u, v;
 34     std::queue <int> q;
 35     memset(dis, -1, sizeof(dis));
 36     q.push(s);
 37     dis[s] = 0;
 38     while(!q.empty())
 39     {
 40         u = q.front(), q.pop();
 41         for(i = head[u]; i ^ -1; i = next[i])
 42         {
 43             v = to[i];
 44             if(val[i] && dis[v] == -1)
 45             {
 46                 dis[v] = dis[u] + 1;
 47                 if(v == t) return 1;
 48                 q.push(v);
 49             }
 50         }
 51     }
 52     return 0;
 53 }
 54 
 55 inline int dfs(int u, int maxflow)
 56 {
 57     if(u == t) return maxflow;
 58     int v, d, ret = 0;
 59     for(int &i = cur[u]; i ^ -1; i = next[i])
 60     {
 61         v = to[i];
 62         if(val[i] && dis[v] == dis[u] + 1)
 63         {
 64             d = dfs(v, min(val[i], maxflow - ret));
 65             ret += d;
 66             val[i] -= d;
 67             val[i ^ 1] += d;
 68             if(ret == maxflow) return ret;
 69         }
 70     }
 71     if(ret ^ maxflow) dis[u] = -1;
 72     return ret;
 73 }
 74 
 75 int main()
 76 {
 77     int i, j, k, x, y;
 78     m = read();
 79     n = read();
 80     s = 0, t = n * m + 1;
 81     memset(head, -1, sizeof(head));
 82     for(i = 1; i <= m; i++)
 83         for(j = 1; j <= n; j++)
 84         {
 85             num++;
 86             sum += x = read();
 87             if((i + j) & 1)
 88             {
 89                 add(s, num, x), add(num, s, 0);
 90                 if(i > 1) add(num, num - n, INF), add(num - n, num, 0);
 91                 if(i < m) add(num, num + n, INF), add(num + n, num, 0);
 92                 if(j > 1) add(num, num - 1, INF), add(num - 1, num, 0);
 93                 if(j < n) add(num, num + 1, INF), add(num + 1, num, 0);
 94             }
 95             else add(num, t, x), add(t, num, 0);
 96         }
 97     while(bfs())
 98     {
 99         for(i = s; i <= t; i++) cur[i] = head[i];
100         sum -= dfs(s, INF);
101     }
102     printf("%d\n", sum);
103     return 0;
104 }