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Add One to Digit Array | Intuit Coding Question

Add One to Digit Array

Company: Intuit

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: easy

Interview Round: Technical Screen

You are given an array of decimal digits representing a non-negative integer. The most significant digit is at index 0, and the array contains no leading zeros unless the number is exactly 0. Add 1 to the represented integer and return the resulting digit array. Examples: - Input: `[1, 2, 3]` → Output: `[1, 2, 4]` - Input: `[1, 2, 9]` → Output: `[1, 3, 0]` - Input: `[9, 9, 9]` → Output: `[1, 0, 0, 0]` Follow-up: The array may be extremely large. You must not convert the entire array to a built-in integer type. Discuss how your approach changes if the array is too large to fit comfortably in memory.

Quick Answer: This question evaluates proficiency in array manipulation and elementary arithmetic on digit sequences, specifically carrying operations and edge-case handling for overflow.

Part 1: Add One to a Digit Array

You are given a list of decimal digits representing a non-negative integer. The most significant digit is at index 0. The list contains no leading zeros unless the number is exactly 0. Add 1 to the represented integer and return the resulting digit list. You must not convert the entire digit list into a built-in integer type. For this problem, an empty list is allowed and represents 0.

Constraints

0 <= len(digits) <= 1000000
Each element of digits is an integer between 0 and 9.
digits has no leading zeros unless digits == [0].
An empty list represents 0.
Do not convert the entire digit array to a built-in integer.

Examples

Input: ([1, 2, 3],)

Expected Output: [1, 2, 4]

Explanation: 123 + 1 = 124.

Input: ([1, 2, 9],)

Expected Output: [1, 3, 0]

Explanation: The final 9 becomes 0 and carries 1 to the 2.

Input: ([9, 9, 9],)

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

Explanation: All digits carry, so the result needs one extra digit.

Input: ([0],)

Expected Output: [1]

Explanation: The number 0 plus 1 is 1.

Input: ([],)

Expected Output: [1]

Explanation: By problem definition, an empty digit array represents 0.

Hints

Addition by 1 only affects digits starting from the least significant digit.
A digit 9 becomes 0 and passes a carry to the digit on its left.

Part 2: Add One to a Huge Chunked Digit Stream

You need to add 1 to a non-negative integer that may be too large to store comfortably as a normal digit array or convert to a built-in integer. The number is provided as decimal string chunks in least-significant-chunk-first order, which is the order you could get by reading fixed-size blocks from the end of a large file. Each chunk contains decimal digits. All chunks except the most significant chunk are fixed-width and may contain leading zeros. The most significant chunk has no leading zeros unless the whole number is 0. Return the resulting number in the same chunked, least-significant-chunk-first representation. For this problem, an empty chunk list represents 0.

Constraints

0 <= len(chunks) <= 1000000
Each chunk is a non-empty string of decimal digits, except that chunks may be empty to represent 0.
Chunks are ordered from least significant to most significant.
All chunks except the most significant chunk have the same width.
Lower chunks may contain leading zeros; the most significant chunk has no leading zeros unless the number is exactly 0.
Do not concatenate all chunks or convert the entire number to a built-in integer.

Examples

Input: (['789', '456', '123'],)

Expected Output: ['790', '456', '123']

Explanation: The chunks represent 123456789. Adding 1 only changes the least significant chunk.

Input: (['999', '129'],)

Expected Output: ['000', '130']

Explanation: The chunks represent 129999. The lower chunk overflows from 999 to 000 and carries into 129.

Input: (['999', '999'],)

Expected Output: ['000', '000', '1']

Explanation: 999999 + 1 = 1000000, requiring a new most significant chunk.

Input: (['009', '1'],)

Expected Output: ['010', '1']

Explanation: The chunks represent 1009. The lower chunk keeps its fixed width after incrementing.

Input: ([],)

Expected Output: ['1']

Explanation: By problem definition, an empty chunk list represents 0.

Hints

The carry from adding 1 moves from the least significant side toward the most significant side.
A chunk made entirely of 9s becomes all 0s and keeps the carry; otherwise, increment the rightmost non-9 digit in that chunk and stop carrying.

Quick Overview

This question evaluates proficiency in array manipulation and elementary arithmetic on digit sequences, specifically carrying operations and edge-case handling for overflow.