Basics and Reverse A Linked List

Question

Given a linked list, return it in reverse.

Verify the constraints

• What do we return if we get null or a single node? - Just return null and the node back respectively.

Write out some test cases

1. 1,2,3,4,5,null => 5,4,3,2,1,null
2. 1 => 1
3. null => null

Figure out a solution without code

• We won't know the full length of the linked list unless we traverse it! - so we have to implement iterative technique

Write out our solution in code

class ListNode{
	constructor(val, next = null){
		this.val = val;
		this.next = next;
	}
}
const linkedList = [5,4,3,2,1].reduce((acc, val) => new ListNode(val, acc), null);
const printList = (head) => {
	let result = "";
        let curNode = head;
        while (curNode !== null) {
            result += curNode.val + "--> ";
            curNode = curNode.next;
        }
        return result;
}
function getReversedLinkedList(head){
	let curNode = head;
	let prevNode = null;
	while(curNode){
		const next = curNode.next;
		curNode.next = prevNode;
		 prevNode = curNode;
		curNode = next;
	}
	head = prevNode;
	return head;
}
console.log(printList(linkedList));
console.log(printList(getReversedLinkedList(linkedList)))

Analyze Space and Time Complexity

• Time Complexity: O(N)
• Space Complexity: O(1)

Developing References

Developing Report

2025-01-23 - Basics and Reverse A Linked List Report
2025-01-23 - Developing Daily Report
2025-01-4th - Developing Weekly Report