[Amazon] Find loop in a singly linkedlist

转载于 2015-08-21 02:21:06 发布 · 487 阅读

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#亚马逊 #linkedlist #算法

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本文介绍了一种使用快慢指针的方法来检测链表中是否存在循环的算法。此方法由Floyd提出，通过设置一个快指针和一个慢指针，快指针每次移动两步，慢指针每次移动一步。如果链表中存在循环，则快慢指针最终会在循环内相遇；反之，若快指针到达链表尾部则表明链表无循环。

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As the title says

http://stackoverflow.com/questions/2663115/how-to-detect-a-loop-in-a-linked-list
Floyd’s cycle-finding algorithm
Having a fast and slow pointer

boolean hasLoop(Node first) {

    if(first == null) // list does not exist..so no loop either.
        return false;

    Node slow, fast; // create two references.

    slow = fast = first; // make both refer to the start of the list.

    while(true) {

        slow = slow.next;          // 1 hop.

        if(fast.next != null)
            fast = fast.next.next; // 2 hops.
        else
            return false;          // next node null => no loop.

        if(slow == null || fast == null) // if either hits null..no loop.
            return false;

        if(slow == fast) // if the two ever meet...we must have a loop.
            return true;
    }
}