dfs染色法, 若存在起点与终点颜色一样则不属于二分图,若全部满足不相同则是, 颜色只有两种.也就是相邻的点颜色属于不同种即可
例题：https://hihocoder.com/problemset/problem/1121
1 #include<stdio.h> 2 #include<string.h> 3 #define mem(a, b) memset(a, b, sizeof(a)) 4 5 int n, m; 6 int head[10010], cnt; 7 int color[10010]; 8 int flag, c; 9 10 struct Edge 11 { 12 int to, next; 13 }edge[40010 * 2]; 14 15 void add(int a, int b) 16 { 17 edge[++ cnt].to = b; 18 edge[cnt].next = head[a]; 19 head[a] = cnt; 20 } 21 22 void dfs(int now, int c) 23 { 24 color[now] = c; //染成c 25 for(int i = head[now]; i != -1; i = edge[i].next) 26 { 27 int to = edge[i].to; 28 if(color[to] == c) 29 { 30 flag = 0; 31 return ; 32 } 33 if(!color[to]) 34 dfs(to, -c); 35 if(!flag) 36 return ; 37 } 38 return ; 39 } 40 41 int main() 42 { 43 int T; 44 scanf("%d", &T); 45 while(T --) 46 { 47 flag = 1; 48 cnt = 0; 49 c = 1; 50 mem(head, -1); 51 mem(color, 0); //染色初始化为0代表没有染色 52 scanf("%d%d", &n, &m); 53 for(int i = 1; i <= m; i ++) 54 { 55 int a, b; 56 scanf("%d%d", &a, &b); 57 add(a, b); 58 add(b, a); 59 } 60 for(int i = 1; i <= n; i ++)//防止不连通图 61 if(!color[i]) 62 { 63 dfs(i, c); 64 if(!flag) 65 break; 66 } 67 if(flag) 68 printf("Correct "); 69 else 70 printf("Wrong "); 71 } 72 return 0; 73 }