0141-linked-list-cycle.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 * int val;
 * ListNode *next;
 * ListNode(int x) : val(x), next(NULL) {}
 * };
*/
classSolution {
public:
 unordered_map<ListNode*,int> mp;
boolhasCycle(ListNode *head) {
while(head != NULL){
if(mp.find(head) == mp.end()){
 ++mp[head];
 }
else{
returntrue;
 }
 head = head->next;
 }
returnfalse;
 }
};