0002.go

// Source: https://leetcode.com/problems/add-two-numbers
// Title: Add Two Numbers
// Difficulty: Medium
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
//
// You may assume that each input would have exactly one solution, and you may not use the same element twice.
//
// You can return the answer in any order.
//
// Example 1:
//
//   Input: nums = [2,7,11,15], target = 9
//   Output: [0,1]
//   Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
//
// Example 2:
//
//   Input: nums = [3,2,4], target = 6
//   Output: [1,2]
//
// Example 3:
//
//   Input: nums = [3,3], target = 6
//   Output: [0,1]
//
// Constraints:
//
//   2 <= nums.length <= 10^4
//   -10^9 <= nums[i] <= 10^9
//   -10^9 <= target <= 10^9
//   Only one valid answer exists.
//
// Follow-up: Can you come up with an algorithm that is less than O(n^2) time complexity?
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package main

// Definition for singly-linked list.
type ListNode struct {
	Val  int
	Next *ListNode
}

func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
	root := &ListNode{Val: l1.Val + l2.Val}

	l3 := root
	l1 = l1.Next
	l2 = l2.Next

	carry := l3.Val / 10
	l3.Val %= 10

	for l1 != nil || l2 != nil {
		l3.Next = &ListNode{Val: carry}
		l3 = l3.Next
		if l1 != nil {
			l3.Val += l1.Val
			l1 = l1.Next
		}
		if l2 != nil {
			l3.Val += l2.Val
			l2 = l2.Next
		}
		carry = l3.Val / 10
		l3.Val %= 10
	}

	if carry != 0 {
		l3.Next = &ListNode{Val: carry}
	}

	return root
}