How do you solve Add to Array-Form of Integer on LeetCode?

Add to Array-Form of Integer (LeetCode #989) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Simulating addition digit by digit is more efficient than converting to integers.

What is the brute force solution for Add to Array-Form of Integer?

The brute force approach for Add to Array-Form of Integer is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves converting the array-form of the integer into an actual integer, adding the integer k, and then converting the result back into an array-form. This is straightforward but not efficient for large inputs. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Add to Array-Form of Integer?

Add to Array-Form of Integer uses the following concepts: Array, Math. The recommended patterns to study are: Array, Math.

What are the interview tips for Add to Array-Form of Integer?

Explain your thought process clearly as you code. Consider edge cases, like when k is larger than the number represented by num. Practice similar problems to build confidence in handling arrays and arithmetic.

What are common mistakes when solving Add to Array-Form of Integer?

Forgetting to handle the carry after processing all digits. Not reversing the result array before returning.

#989

Add to Array-Form of Integer

Easy

ArrayMathArrayMath

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

The optimal solution directly simulates the addition process digit by digit, handling carries as we would in manual addition. This avoids the overhead of converting to and from integers, making it efficient.

⚙️

Algorithm

5 steps

1Step 1: Initialize an empty result array and a carry variable set to 0.
2Step 2: Start from the least significant digit (the end of the num array) and add each digit to k, along with any carry from the previous addition.
3Step 3: If the sum is 10 or more, calculate the new carry and store the digit in the result.
4Step 4: Continue until all digits in num and k are processed, including any remaining carry.
5Step 5: Reverse the result array to get the final answer in the correct order.

solution.py15 lines

1# Full working Python code
2num = [1, 2, 0, 0]
3k = 34
4result = []
5carry = k
6for digit in reversed(num):
7    total = digit + carry
8    result.append(total % 10)
9    carry = total // 10
10if carry > 0:
11    while carry > 0:
12        result.append(carry % 10)
13        carry //= 10
14result.reverse()
15print(result)

ℹ

Complexity note: The time complexity is O(n) because we iterate through the digits of num once, and the space complexity is O(n) due to the result array storing the digits.

1Simulating addition digit by digit is more efficient than converting to integers.
2Handling carries is crucial in addition problems.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.