Linked List Patterns

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public int fn(ListNode head) {
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    ListNode slow = head;
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    ListNode fast = head;
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    int ans = 0;
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    while (fast != null && fast.next != null) {
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        // TODO: logic
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        slow = slow.next;
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        fast = fast.next.next;
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    }
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    return ans;
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}

1
public ListNode fn(ListNode head) {
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    ListNode curr = head;
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    ListNode prev = null;
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    while (curr != null) {
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        ListNode nextNode = curr.next;
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        curr.next = prev;
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        prev = curr;
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        curr = nextNode;
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    }
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    return prev;
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}