Add to Array-Form of Integer - Easy - LeetCode

For a non-negative integer X, the array-form of X is an array of its digits in left to right order. For example, if X = 1231, then the array form is [1,2,3,1].

Given the array-form A of a non-negative integer X, return the array-form of the integer X+K.

Example 1:

Input: A = [1,2,0,0], K = 34

Output: [1,2,3,4]

Explanation: 1200 + 34 = 1234

Example 2:

Input: A = [2,7,4], K = 181

Output: [4,5,5]

Explanation: 274 + 181 = 455

Example 3:

Input: A = [2,1,5], K = 806

Output: [1,0,2,1]

Explanation: 215 + 806 = 1021

Example 4:

Input: A = [9,9,9,9,9,9,9,9,9,9], K = 1

Output: [1,0,0,0,0,0,0,0,0,0,0]

Explanation: 9999999999 + 1 = 10000000000

Note：

1 <= A.length <= 10000

0 <= A[i] <= 9

0 <= K <= 10000

If A.length > 1, then A[0] != 0

Solution:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LeetCode.AskGif.Easy.Array
{
 public class AddToArrayFormSoln
 {
 public IList<int> AddToArrayForm(int[] A, int K)
 { 
 var res = new List<int>();
 int i = A.Length - 1;
 int carry = 0;
 int a = 0;
 int b = 0;
 int num = 0;
 while (true)
 {
 a = 0;
 b = 0;

 if (i < 0 && K <= 0)
 {
 break;
 }

 if (i >= 0)
 {
 a = A[i]; 
 }
 i--;

 if (K > 0)
 {
 b = K % 10;
 K = K / 10;
 }

 num = a + b + carry;
 if (num > 9)
 {
 res.Add(num % 10);
 carry = num / 10;
 }
 else
 {
 res.Add(num);
 carry = 0;
 } 
 }

 if(carry > 0)
 {
 res.Add(carry);
 }

 res.Reverse();

 return res;
 }
 }
}

Time Complexity: O(n)

Space Complexity: O(n) to store the result.

Unit Tests:

using LeetCode.AskGif.Easy.Array;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.Array
{
 [TestClass]
 public class AddToArrayFormSolnTests
 {
 [TestMethod]
 public void AddToArrayFormSoln_First()
 {
 var arr = new int[] { 1, 2, 0, 0 };
 var K = 34;
 var expected = new int[] { 1, 2, 3, 4 };

 var res = new AddToArrayFormSoln().AddToArrayForm(arr, K);
 AreEqual(expected, res);
 }

 [TestMethod]
 public void AddToArrayFormSoln_Second()
 {
 var arr = new int[] { 2, 7, 4 };
 var K = 181;
 var expected = new int[] { 4, 5, 5 };

 var res = new AddToArrayFormSoln().AddToArrayForm(arr, K);
 AreEqual(expected, res);
 }

 [TestMethod]
 public void AddToArrayFormSoln_Third()
 {
 var arr = new int[] { 2, 1, 5 };
 var K = 806;
 var expected = new int[] { 1, 0, 2, 1 };

 var res = new AddToArrayFormSoln().AddToArrayForm(arr, K);
 AreEqual(expected, res);
 }

 [TestMethod]
 public void AddToArrayFormSoln_Fourth()
 {
 var arr = new int[] { 9, 9, 9, 9, 9, 9, 9, 9, 9, 9 };
 var K = 1;
 var expected = new int[] { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

 var res = new AddToArrayFormSoln().AddToArrayForm(arr, K);
 AreEqual(expected, res);
 }

 private void AreEqual(int[] res, IList<int> output)
 {
 Assert.AreEqual(res.Length, output.Count);
 for (int i = 0; i < res.Length; i++)
 {
 Assert.AreEqual(res[i], output[i]);
 }
 }
 }
}