http://poj.org/problem?id=2112_网络流

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #include<cstdlib>
 5 #include<algorithm>
 6 using namespace std;
 7 
 8 #define MAX 300
 9 #define INF 10000000
10 int dis[MAX][MAX];  // 任意两点间的最短路径
11 int map[MAX][MAX];  // 容量网络
12 bool sign[MAX][MAX];  // 层次网络
13 bool used[MAX];  // 标志数组
14 int K, C, n, M;
15 
16 void Build_Graph(int min_max) {
17     memset(map, 0, sizeof(map));
18     for(int i=K+1; i<=n; i++) map[0][i] = 1;
19     for(int i=1; i<=K; i++) map[i][n+1] = M;
20     for(int i=K+1; i<=n; i++) {
21         for(int j=1; j<=K; j++) {
22             if(dis[i][j]<=min_max) map[i][j] = 1;
23         }
24     }
25 }
26 bool BFS() {  // BFS构建层次网络
27     // 初始化
28     memset(used, 0, sizeof(used));
29     memset(sign, 0, sizeof(sign));
30     int queue[100*MAX] = {0};
31     queue[0] = 0;
32     used[0] = 1;
33     int t = 1, f = 0;
34     while(f<t) {
35         for(int i=0; i<=n+1; i++) {
36             if(!used[i]&&map[queue[f]][i]) {
37                 queue[t++] = i;
38                 used[i] = 1;
39                 sign[queue[f]][i] = 1;
40             }
41         }
42         f++;
43     }
44     if(used[n+1]) return true;
45     else return false;
46 }
47 int DFS(int v, int sum) {
48     int s, t;
49     if(v==n+1) return sum;
50     s = sum;
51     for(int i=0; i<=n+1; i++) {
52         if(sign[v][i]) {
53             t = DFS(i, min(map[v][i], sum));
54             map[v][i] -= t;
55             map[i][v] += t;
56             sum -= t;
57         }
58     }
59     return s-sum;
60 }
61 int main() {
62     //freopen("test.txt", "r", stdin);
63     int L, R, mid, ans;
64     while(scanf("%d %d %d", &K, &C, &M)!=EOF) {
65         n = K+C;
66         // Floyd求任意两点间的最短距离
67         for(int i=1; i<=n; i++) {
68             for(int j=1; j<=n; j++) {
69                 scanf("%d", &dis[i][j]);
70                 if(dis[i][j]==0) dis[i][j] = INF;
71             }
72         }
73         for(int k=1; k<=n; k++) {
74             for(int i=1; i<=n; i++) {
75                 if(dis[i][k]!=INF) {
76                     for(int j=1; j<=n; j++) dis[i][j] = min(dis[i][k]+dis[k][j], dis[i][j]);
77                 }
78             }
79         }
80         L = 0, R = 10000;
81 
82         // 二分法搜索
83         while(L<R) {
84             mid = (L+R)>>1;
85             ans = 0;
86             // Dinic法求最大流
87             Build_Graph(mid);  // 构建容量网络（残余网络）
88             while(BFS()) ans += DFS(0, INF);  // 构建层次网络，并进行DFS增广
89             if(ans>=C) R = mid;
90             else L = mid+1;
91         }
92         printf("%d\n", R);
93     }
94     return 0;
95 }