LeetCode - Swap Nodes in Pairs
Problem description
Given a linked list, swap every two adjacent nodes and return its head.
You may not modify the values in the list’s nodes, only nodes itself may be changed.
Example:
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Given 1->2->3->4, you should return the list as 2->1->4->3.
Analysis
Basic idea is to divide the LinkedList into two LinkedList and then merge them.
Here’s the code:
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public class SwapNodesinPairs {
public ListNode swapPairs(ListNode head) {
ListNode l1 = new ListNode(0), l2 = new ListNode(0);
ListNode dummy = new ListNode(0);
ListNode p1 = l1, p2 = l2;
boolean flag = true;
while (head != null) {
if (flag) {
p1.next = head;
p1 = p1.next;
head = head.next;
p1.next = null;
flag = false;
} else {
p2.next = head;
p2 = p2.next;
head = head.next;
p2.next = null;
flag = true;
}
}
flag = true;
ListNode p = dummy;
l1 = l1.next;
l2 = l2.next;
while (l1 != null || l2 != null) {
if (flag && l2 != null) {
p.next = l2;
l2 = l2.next;
flag = false;
} else {
p.next = l1;
l1 = l1.next;
flag = true;
}
p = p.next;
}
return dummy.next;
}
}
There’s another solution, which is to swap two nodes in one pass.