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/**
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 * Definition for singly-linked list.
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 * function ListNode(val, next) {
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 *     this.val = (val===undefined ? 0 : val)
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 *     this.next = (next===undefined ? null : next)
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 * }
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 */
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/**
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 * @param {ListNode} head
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 * @return {ListNode}
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 */
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var swapPairs = function(head) {
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    if(!head || !head.next){
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        return head
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    };
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    let header = new ListNode();
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    header.next = head
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    let vnode = header;
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    while(head && head.next){
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        const temp = head.next;
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        head.next = head.next.next;
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        temp.next = head;
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        vnode.next = temp;
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        vnode = head;
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        head = head.next;
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    }
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    return header.next;
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};