Minimum Cost(最小费用最大流)
Description
Dearboy, a goods victualer, now comes to a big problem, and he needs your help. In his sale area there are N shopkeepers (marked from 1 to N) which stocks goods from him.Dearboy has M supply places (marked from 1 to M), each provides K different kinds of goods (marked from 1 to K). Once shopkeepers order goods, Dearboy should arrange which supply place provide how much amount of goods to shopkeepers to cut down the total cost of transport.
It's known that the cost to transport one unit goods for different kinds from different supply places to different shopkeepers may be different. Given each supply places' storage of K kinds of goods, N shopkeepers' order of K kinds of goods and the cost to transport goods for different kinds from different supply places to different shopkeepers, you should tell how to arrange the goods supply to minimize the total cost of transport.
It's known that the cost to transport one unit goods for different kinds from different supply places to different shopkeepers may be different. Given each supply places' storage of K kinds of goods, N shopkeepers' order of K kinds of goods and the cost to transport goods for different kinds from different supply places to different shopkeepers, you should tell how to arrange the goods supply to minimize the total cost of transport.
Input
The input consists of multiple test cases. The first line of each test case contains three integers N, M, K (0 < N, M, K < 50), which are described above. The next N lines give the shopkeepers' orders, with each line containing K integers (there integers are belong to [0, 3]), which represents the amount of goods each shopkeeper needs. The next M lines give the supply places' storage, with each line containing K integers (there integers are also belong to [0, 3]), which represents the amount of goods stored in that supply place.
Then come K integer matrices (each with the size N * M), the integer (this integer is belong to (0, 100)) at the i-th row, j-th column in the k-th matrix represents the cost to transport one unit of k-th goods from the j-th supply place to the i-th shopkeeper.
The input is terminated with three "0"s. This test case should not be processed.
Then come K integer matrices (each with the size N * M), the integer (this integer is belong to (0, 100)) at the i-th row, j-th column in the k-th matrix represents the cost to transport one unit of k-th goods from the j-th supply place to the i-th shopkeeper.
The input is terminated with three "0"s. This test case should not be processed.
Output
For each test case, if Dearboy can satisfy all the needs of all the shopkeepers, print in one line an integer, which is the minimum cost; otherwise just output "-1".
Sample Input
1 3 3 1 1 1 0 1 1 1 2 2 1 0 1 1 2 3 1 1 1 2 1 1 1 1 1 3 2 20 0 0 0
Sample Output
4 -1
题意：有n个商店，m个提供商，k种商品
接下来 n*k的矩阵，表示每个商店需要每个商品的数目；
再接下来m*k矩阵，表示每个提供商拥有每个商品的个数。
然后，对于每个物品k，都有n*m的矩阵。
i行j列表示：
从j提供商向i商店运送一个k商品的代价是多少。
判断所有的仓库能否满足所有客户的需求，如果可以，求出最少的运输总费用。
思路：关键是建图，建立一个源点是s = 0 和 汇点 t = n+m+1;
源点到m个供应商，费用为0，容量是这个提供商能够提供这种物品的数量；
每个供应商到每个商店，费用为输入的费用（添加双向边），容量为无穷大；
每个商店到汇点，费用为0，容量为这个商店需要这种商品的数目。
还要考虑到供不应求的情况，当需求量大于供应量时，不能满足，输出-1.
对于第r种商品，若它的需求量大于最大流量，也不能满足，输出-1；
对每1个商品进行建图寻找增光路，最后累加输出最小费用就行了；
1 #include<stdio.h> 2 #include<string.h> 3 #include<queue> 4 #include<algorithm> 5 using namespace std; 6 7 const int maxn = 200; 8 const int INF = 0x3f3f3f3f; 9 int n,m,k; 10 int nn[maxn][maxn],need[maxn]; 11 int hh[maxn][maxn],have[maxn]; 12 int cost[maxn][maxn],res[maxn][maxn];//cost[i][j]表示i到j的费用，res[i][j]表示i到j的当前容量 13 int s, t; 14 int mincost,maxflow; 15 int dis[maxn],pre[maxn]; 16 void build_graph(int x) 17 { 18 memset(res,0,sizeof(res)); 19 for(int i = 1; i <= m; i++) 20 res[s][i+n] = hh[i][x];//源点指向每个供应商，费用为0，容量为该供应商提供的第r种商品 21 for(int i = 1; i <= n; i++) 22 res[i][t] = nn[i][x];//所有商店指向汇点，费用为0，容量为该供应商需要的第r种商品 23 for(int i = 1; i <= m; i++) 24 { 25 for(int j = 1; j <= n; j++) 26 res[i+n][j] = INF;//每个供应商指向每个商店，容量为无穷大。 27 } 28 } 29 void spfa() 30 { 31 queue<int>que; 32 while(!que.empty()) 33 que.pop(); 34 memset(pre,-1,sizeof(pre)); 35 int inque[maxn]; 36 memset(inque,0,sizeof(inque)); 37 for(int i = s; i <= t; i++) 38 dis[i] = INF; 39 dis[s] = 0; 40 inque[s] = 1; 41 que.push(s); 42 43 while(!que.empty()) 44 { 45 int u = que.front(); 46 que.pop(); 47 inque[u] = 0; 48 49 for(int i = 0; i <= n+m+1; i++) 50 { 51 if(res[u][i] && dis[i] > dis[u] + cost[u][i]) 52 { 53 dis[i] = dis[u] + cost[u][i]; 54 pre[i] = u; 55 if(!inque[i]) 56 { 57 inque[i] = 1; 58 que.push(i); 59 } 60 } 61 } 62 } 63 } 64 65 void MCMF() 66 { 67 maxflow = 0;//增光第r种商品的总流量，初始化为0； 68 int minflow;//当前增光路上可增加的最小流量； 69 while(1) 70 { 71 spfa(); 72 if(pre[t] == -1)//找不到增光路，退出 73 break; 74 75 minflow = INF; 76 for(int u = t; u != s; u = pre[u]) 77 { 78 minflow = min(minflow,res[ pre[u] ][u]);//寻找该增光路上的最小流量 79 } 80 for(int u = t; u != s; u = pre[u]) 81 { 82 res[ pre[u] ][u] -= minflow; 83 res[u][ pre[u] ] += minflow; 84 } 85 maxflow += minflow; 86 mincost += minflow*dis[t]; 87 } 88 } 89 90 int main() 91 { 92 while(~scanf("%d %d %d",&n,&m,&k)) 93 { 94 if(n == 0 && m == 0 && k == 0) 95 break; 96 bool flag = 0; 97 s = 0;//源点 98 t = n+m+1;//汇点 99 mincost = 0;//最小费用初始化； 100 memset(need,0,sizeof(need)); 101 memset(have,0,sizeof(have)); 102 //nn[i][j]表示第i个商店需求nn[i][j]个第j种商品； 103 for(int i = 1; i <= n; i++) 104 { 105 for(int j = 1; j <= k; j++) 106 { 107 scanf("%d",&nn[i][j]); 108 need[j] += nn[i][j]; 109 } 110 } 111 //hh[i][j]表示第i个供应商拥有hh[i][j]个第j中商品； 112 for(int i = 1; i <= m; i++) 113 { 114 for(int j = 1; j <= k; j++) 115 { 116 scanf("%d",&hh[i][j]); 117 have[j] += hh[i][j]; 118 } 119 } 120 //如果第i种商品的需求量大于供应量，标记为1，但后面的仍然要继续输入 121 for(int i = 1; i <= k; i++) 122 { 123 if(need[i] > have[i]) 124 { 125 flag = 1; 126 break; 127 } 128 } 129 //下面输入k个n*m的矩阵，其第i行第j列表示第j个供应商向第i个商店运送第k个商品的单位费用； 130 for(int r = 1; r <= k; r++) 131 { 132 memset(cost,0,sizeof(cost)); 133 for(int i = 1; i <= n; i++) 134 { 135 for(int j = 1; j <= m; j++) 136 { 137 scanf("%d",&cost[j+n][i]); 138 cost[i][j+n] = -cost[j+n][i];//注意添加双向边 139 } 140 } 141 if(flag) continue;//如果已经不合法，就不用建图，但数据要继续输入 142 143 build_graph(r); 144 MCMF(); 145 if(need[r] > maxflow) flag = 1;//如果第r种商品的需求量大于最大流量，也不合法。 146 } 147 if(flag) printf("-1\n"); 148 else printf("%d\n",mincost); 149 } 150 return 0; 151 }