Swap Nodes in Pairs
描述
Given a linked list, swap every two adjacent nodes and return its head.
For example,
Given 1->2->3->4, you should return the list as 2->1->4->3.
Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.
分析
无
代码
// Swap Nodes in Pairs
// 时间复杂度O(n)，空间复杂度O(1)
class Solution {
public ListNode swapPairs(ListNode head) {
if (head == null || head.next == null) return head;
ListNode dummy = new ListNode(-1);
dummy.next = head;
for(ListNode prev = dummy, cur = prev.next, next = cur.next;
next != null;
prev = cur, cur = cur.next, next = cur != null ? cur.next: null) {
prev.next = next;
cur.next = next.next;
next.next = cur;
}
return dummy.next;
}
}下面这种写法更简洁，但题目规定了不准这样做。
// Swap Nodes in Pairs
// 时间复杂度O(n)，空间复杂度O(1)
class Solution {
public ListNode swapPairs(ListNode head) {
ListNode p = head;
while (p != null && p.next != null) {
int tmp = p.val;
p.val = p.next.val;
p.next.val = tmp;
p = p.next.next;
}
return head;
}
}