Swap Nodes in Pairs

1. Problem Description

Given a linked list, swap every two adjacent nodes and return the head of the modified list. You must solve the problem without modifying node values (only node links may be changed).

2. Approach

Same as Reverse Linked List II

3. Implementation

3.1. Three Pointers

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func swapPairs(head *ListNode) *ListNode {
    if head == nil || head.Next == nil { return head }
    dummyHead := &ListNode{}
    d := dummyHead
    current := head
    for current != nil {
        var next *ListNode
        d.Next,next = reverse(current, 2)
        d = d.Next.Next
        current = next
    }
    return dummyHead.Next
}

func reverse(head *ListNode, count int) (*ListNode, *ListNode) {
    if head == nil || head.Next == nil {return head, nil}
    var prev *ListNode
    current := head
    var next *ListNode
    for i:=0;i < count;i++ {
        next = current.Next
        current.Next = prev
        prev = current
        current = next
    }
    return prev, current
}

4. References

• 24. Swap Nodes in Pairs - LeetCode