Add Two Numbers

Description

original description

Solutions

Clear Version

simulate the calculation

function ListNode(val, next) {
  this.val = val === undefined ? 0 : val;
  this.next = next === undefined ? null : next;
}

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function (l1, l2) {
  const head = new ListNode();
  let current = head;
  let carry = 0;

  while (l1 && l2) {
    const sum = l1.val + l2.val + carry;
    const val = sum % 10;
    carry = Math.floor(sum / 10);

    current.next = new ListNode(val);
    current = current.next;
    l1 = l1.next;
    l2 = l2.next;
  }

  while (l1) {
    const sum = l1.val + carry;
    const val = sum % 10;
    carry = Math.floor(sum / 10);

    current.next = new ListNode(val);
    current = current.next;
    l1 = l1.next;
  }

  while (l2) {
    const sum = l2.val + carry;
    const val = sum % 10;
    carry = Math.floor(sum / 10);

    current.next = new ListNode(val);
    current = current.next;
    l2 = l2.next;
  }

  if (carry) {
    current.next = new ListNode(carry);
  }

  return head.next;
};

• Time Complexity: O(n)
• Space Complexity: O(n)

Merge Calculation

function ListNode(val, next) {
  this.val = val === undefined ? 0 : val;
  this.next = next === undefined ? null : next;
}

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function (l1, l2) {
  const head = new ListNode();
  let current = head;
  let carry = 0;

  while (l1 || l2) {
    const sum = (l1?.val ?? 0) + (l2?.val ?? 0) + carry;    // the new syntax
    const val = sum % 10;
    carry = Math.floor(sum / 10);

    current.next = new ListNode(val);
    current = current.next;
    l1 = l1?.next;
    l2 = l2?.next;
  }

  if (carry) {
    current.next = new ListNode(carry);
  }

  return head.next;
};

• Time Complexity: O(n)
• Space Complexity: O(n)