Poj--3041（二分图最大匹配，最小点覆盖）

2014-11-04 22:57:48

思路：König定理：最小覆盖点数==最大匹配数。证明：推荐Matrix67（虽然还没全看懂QAQ）http://www.matrix67.com/blog/archives/116

 1 /*************************************************************************
 2     > File Name: 3041.cpp
 3     > Author: Nature
 4     > Mail: 564374850@qq.com 
 5     > Created Time: Tue 04 Nov 2014 09:37:54 PM CST
 6 ************************************************************************/
 7 
 8 #include <cstdio>
 9 #include <cstring>
10 #include <cstdlib>
11 #include <cmath>
12 #include <vector>
13 #include <map>
14 #include <set>
15 #include <stack>
16 #include <queue>
17 #include <iostream>
18 #include <algorithm>
19 using namespace std;
20 #define lp (p << 1)
21 #define rp (p << 1|1)
22 #define getmid(l,r) (l + (r - l) / 2)
23 #define MP(a,b) make_pair(a,b)
24 typedef long long ll;
25 const int INF = 1 << 30;
26 const int maxn = 510;
27 
28 int n,k;
29 int first[maxn],next[maxn * maxn],ver[maxn * maxn],ecnt;
30 int mat[maxn],used[maxn];
31 
32 void Init(){
33     memset(first,-1,sizeof(first));
34     ecnt = 0;
35 }
36 
37 void Add_edge(int u,int v){
38     next[++ecnt] = first[u];
39     ver[ecnt] = v;
40     first[u] = ecnt;
41 }
42 
43 bool find(int p){
44     for(int i = first[p]; i != -1; i = next[i]){
45         int v = ver[i];
46         if(used[v] == 0){
47             used[v] = 1;
48             if(mat[v] == 0 || find(mat[v])){
49                 mat[v] = p;
50                 return true;
51             }
52         }
53     }
54     return false;
55 }
56 
57 int Hungary(){
58     int ans = 0;
59     for(int i = 1; i <= n; ++i){
60         memset(used,0,sizeof(used));
61         if(find(i)) ++ans;
62     }
63     return ans;
64 }
65 
66 int main(){
67     int a,b;
68     while(scanf("%d%d",&n,&k) != EOF){
69         Init();
70         for(int i = 1; i <= k; ++i){
71             scanf("%d%d",&a,&b);
72             Add_edge(a,b);
73         }
74         printf("%d\n",Hungary());
75     }
76     return 0;
77 }

 

posted @ 2014-11-04 22:59  Naturain  阅读(142)  评论(0)    收藏  举报