algorithm/Week_01/id_1/LeetCode_24_1.java at master · feixiangcode/algorithm · GitHub

44 lines (32 loc) · 865 Bytes

class Solution {

ListNode prePairTail = null;

public ListNode swapPairs(ListNode head) {

if (head == null) {

return null;

}

if (head.next == null) {

return head;

}

ListNode result = head.next;

ListNode node = head;

ListNode next = head.next;

while (node != null && next != null) {

node = swap(node, next);

if (node == null) {

break;

}

next = node.next;

}

return result;

}

private ListNode swap(ListNode node, ListNode next) {

ListNode tmpNext = next.next;

next.next = node;

node.next = tmpNext;

if (prePairTail != null) {

prePairTail.next = next;

}

prePairTail = node;

return tmpNext;

}

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