tags: leetcode
Introduce:
Given the head of a singly linked list, reverse the list, and return the reversed list.
Example 1:
Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]
Example 2:
Input: head = [1,2]
Output: [2,1]
Example 3:
Input: head = []
Output: []
Constraints:
The number of nodes in the list is the range [0, 5000].
-5000 <= Node.val <= 5000
tips:
curr to record the old linkedlist's pointer.
prev to record the new linkedlist's pointer.
next to record curr's next so the old pointer won't be lost.
| prev | curr | next |
|---|---|---|
| null | 1 | 2 |
| 1 | 2 | 3 |
| 2 | 3 | 4 |
| 3 | 4 | 5 |
| 4 | 5 | null |
| 5 | null | X |
var reverseList = function(head) {
let prev, next, curr;
prev = null;
curr = head;
while(curr){
//save curr.next
next = curr.next;
//curr.next point to prev
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
};
