g0101_0200.s0141_linked_list_cycle.Solution.cpp Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

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// #Easy #Top_100_Liked_Questions #Top_Interview_Questions #Hash_Table #Two_Pointers #Linked_List
// #Data_Structure_I_Day_7_Linked_List #Udemy_Linked_List #Big_O_Time_O(N)_Space_O(1)
// #2024_05_27_Time_7_ms_(84.60%)_Space_10.7_MB_(18.04%)

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    bool hasCycle(ListNode* head) {
        if (head == nullptr) {
            return false;
        }
        ListNode* fast = head->next;
        ListNode* slow = head;
        while (fast != nullptr && fast->next != nullptr) {
            if (fast == slow) {
                return true;
            }
            fast = fast->next->next;
            slow = slow->next;
        }
        return false;
    }
};