二分图

二分图判定：二着色

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <vector>
 5 using namespace std;
 6 
 7 int T;
 8 int N, M;
 9 int c[10001];
10 bool visit[10001];
11 vector<vector<int> > m;
12 
13 bool bfs(int idx, int flag) {
14     visit[idx] = true;
15     c[idx] = flag;
16     for (int i = 0; i < m[idx].size(); ++i) {
17         if (c[m[idx][i]] == c[idx]) return false;
18         else c[m[idx][i]] = -flag;
19     }
20     for (int i = 0; i < m[idx].size(); ++i) {
21         if (!visit[m[idx][i]] && !bfs(m[idx][i], -flag))
22             return false;
23     }
24     return true;
25 }
26 
27 void solve() {
28     memset(c, 0, sizeof(c));
29     memset(visit, false, sizeof(visit));
30     for (int i = 0; i < N; ++i) {
31         if (!visit[i] && !bfs(i, 1)) {
32             cout << "Wrong" << endl;
33             return;
34         }
35     }
36     cout << "Correct" << endl;
37 }
38 
39 int main() {
40     cin >> T;
41     for (int t = 0; t < T; ++t) {
42         m.clear();
43         cin >> N >> M;
44         m.resize(N + 1);
45         int u, v;
46         for (int i = 0; i < M; ++i) {
47             cin >> u >> v;
48             m[u].push_back(v);
49             m[v].push_back(u);
50         }
51         solve();
52     }
53     return 0;
54 }

二分图最大匹配：Hungary算法

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 
 4 int N, M;
 5 vector<vector<int>> graph;
 6 vector<int> link;
 7 vector<bool> visited;
 8 int a, b;
 9 
10 int dfs(int u) {
11     for (auto v : graph[u]) if (!visited[v]) {
12         visited[v] = true;
13         if (link[v] == -1 || dfs(link[v])) {
14             link[v] = u;
15             return 1;
16         }
17     }
18     return 0;
19 }
20 
21 int hungary() {
22     int res = 0;
23     for (int i = 0; i <= N; ++i) {
24         visited.assign(N + 1, false);
25         res += dfs(i);
26     }
27     return res / 2;
28 }
29 
30 int main() {
31     while (cin >> N >> M) {
32         graph.assign(N + 1, vector<int>());
33         link.assign(N + 1, -1);
34         for (int i = 0; i < M; ++i) {
35             cin >> a >> b;
36             graph[a].push_back(b);
37             graph[b].push_back(a);
38         }
39         int res = hungary();
40         cout << res << endl;
41     }
42     return 0;
43 }

 

转载于:https://www.cnblogs.com/easonliu/articles/4575475.html