Detect a loop in a Linked List

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• stackqueuelinkedlist
• linkedlist
• loop
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• Posted: 7 years ago

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• answers (1)
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public boolean  hasLoop(Node first){

      /* Linked List doesn't exist - so no loop */
      if(first == null)
          return false;

      /* Create two reference */
      Node slow, fast;

      /* Both start from the beginning of the Linked List */
      slow = fast = first;
      while(true){
          /* One hop */
          slow = slow.next;
          if(fast.next! = null)
              /* Two hops */
              fast = fast.next.next;
          else
              return false;

          /* If slow or fast either hits null - no loop */
          if(slow == null || fast == null)
              return false;

          /* if slow and fast meet - Bingo! loop found */
          if(slow == fast)
              return true;
      }
  }