二分图判定

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <iostream>
 4 #include <queue>
 5 #define maxn 1010
 6 using namespace std;
 7 
 8 int n, m;
 9 int col[maxn];
10 int mp[maxn][maxn];
11 bool isbg;
12 
13 // bfs 判断是不是二分图
14 bool bfscol(int id) {
15     queue<int>que;
16     que.push(id);
17     col[id] = 1;
18 
19     while (!que.empty()) {
20         int top = que.front();
21         que.pop();
22         for (int j=1; j<=n; ++j) {
23             if (mp[top][j]) {
24                 if (col[j] == -1) {
25                     col[j] = (col[top]^1);
26                     que.push(j);
27                 }
28                 else if (col[j] == col[top]) {
29                     return false;
30                 }
31             }
32         }
33     }
34     return true;
35 }
36 
37 int main() {
38     while(cin >> n >> m) {
39         memset(mp, 0, sizeof(mp));
40         for (int i=0; i<m; ++i) {
41             int x, y;
42             cin >> x >> y;
43             mp[x][y] = 1;
44             mp[y][x] = 1;
45         }
46 
47         isbg = true;
48         memset(col, -1, sizeof(col));
49 
50         for (int i=1; i<=n; ++i) {
51             if (col[i] != -1) continue;
52             else if (!bfscol(i)) {
53                 isbg = false;
54                 break;
55             }
56         }
57 
58         if (!isbg) {
59             cout << "No\n";
60             continue;
61         }
62         else cout << "Yes\n";
63     }
64     return 0;
65 }

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <iostream>
 4 #define maxn 1010
 5 using namespace std;
 6 
 7 int n, m;
 8 int col[maxn];
 9 int mp[maxn][maxn];
10 bool isbg;
11 
12 // dfs 判断是否是二分图
13 void dfs_col(int i, int c) {
14     if (!isbg) return; // 剪枝
15     col[i] = c;
16 
17     for (int j=1; j<=n; ++j) {
18         if (mp[i][j]) { // 所有相邻的点
19             if (col[j] == -1) { // 染上不同的颜色
20                 dfs_col(j, c^1);
21             }
22             else if (col[j] == c) { // 如果相邻点颜色相同 不是二分图
23                 isbg = false;
24                 return;
25             }
26         }
27     }
28     return;
29 }
30 
31 int main() {
32     while(cin >> n >> m) {
33         memset(mp, 0, sizeof(mp));
34         for (int i=0; i<m; ++i) {
35             int x, y;
36             cin >> x >> y;
37             mp[x][y] = 1;
38             mp[y][x] = 1;
39         }
40 
41         isbg = true;
42         memset(col, -1, sizeof(col));
43 
44        for (int i=1; i<=n; ++i) {
45             if (col[i] != -1) continue;
46             dfs_col(i, 1);
47             if (isbg == false)
48             break;
49         }
50 
51         if (!isbg) {
52             cout << "No\n";
53             continue;
54         }
55         else cout << "Yes\n";
56     }
57     return 0;
58 }