0141Linked_List_Cycle.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
#pragma GCC optimize("Ofast","inline","ffast-math","unroll-loops","no-stack-protector")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native","f16c")
class Solution {
public:
    bool hasCycle(ListNode *head) {
        ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
        ListNode* slow = head;
        ListNode* fast = head;
        while (fast && fast->next) {
        slow = slow->next;
        fast = fast->next->next;
        if (slow == fast)
            return true;
        }
        return false;
    }
};