Linked List Cycle LeetCode solution in C++

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class Solution {
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 public:
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  bool hasCycle(ListNode *head) {
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    // if head is NULL then return false;
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    if (head == NULL) return false;
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    // making two pointers fast and slow and assignning them to head
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    ListNode *fast = head;
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    ListNode *slow = head;
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    // till fast and fast-> next not reaches NULL
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    // we will increment fast by 2 step and slow by 1 step
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    while (fast != NULL && fast->next != NULL) {
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      fast = fast->next->next;
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      slow = slow->next;
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      // At the point if fast and slow are at same address
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      // this means linked list has a cycle in it.
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      if (fast == slow) return true;
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    }
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    // if traversal reaches to NULL this means no cycle.
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    return false;
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  }
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};