笔试算法题（27）：判断单向链表是否有环并找出环入口节点 & 判断两棵二元树是否相等

 1 struct Node {
 2         int v;
 3         Node *next;
 4 };
 5 Node* IsCycle(Node *head) {
 6         Node *fast=head, *slow=head;
 7 
 8         while(true) {
 9                 if(fast!=NULL)
10                         fast=fast->next;
11                 if(fast!=NULL)
12                         fast=fast->next;
13                 else
14                         return NULL;
15                 if(slow!=NULL)
16                         slow=slow->next;
17                 else
18                         return NULL;
19 
20                 if(fast==slow)
21                         return fast;
22         }
23 }
24 Node* FindEntry(Node *head, Node *joint) {
25         Node *m=head, *n=joint;
26         while(true) {
27                 if(m==n)
28                         return m;
29                 m=m->next;
30                 n=n->next;
31         }
32 }
33 int main() {
34         Node* b1=new Node(); b1->v=1;
35         Node* b2=new Node(); b2->v=2;b1->next=b2;
36         Node* b3=new Node(); b3->v=3;b2->next=b3;
37         Node* b4=new Node(); b4->v=4;b3->next=b4;
38         Node* b5=new Node(); b5->v=5;b4->next=b5;
39         Node* b6=new Node(); b6->v=6;b5->next=b6;
40         Node* b7=new Node(); b7->v=7;b6->next=b7;
41         Node* b8=new Node(); b8->v=8;b7->next=b8; b8->next=b3;
42 
43         Node* temp;
44         if((temp=IsCycle(b1))!=NULL) {
45                 printf("\nthe joint point is: %d",temp->v);
46                 printf("\nthe entry of cycle is: %d",FindEntry(b1,temp)->v);
47         }
48         else
49                 printf("\nthere is no cycle.");
50         return 0;
51 }

 1 struct Node {
 2         int value;
 3         Node *left;
 4         Node *right;
 5 };
 6 
 7 bool CompareTree(Node *first, Node *second) {
 8         if(first==NULL && second==NULL)
 9                 return true;
10         if((first==NULL && second!=NULL) ||
11                         (first!=NULL && second==NULL))
12                 return false;
13         if(first->value!=second->value)
14                 return false;
15         return CompareTree(first->left,second->left) &&
16                         CompareTree(first->right, second->right);
17 }