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This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Bytedance.

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This question is commonly asked for Software Engineer candidates at Bytedance during technical interviews.

Solve String Addition and Expression Evaluation

Company: Bytedance

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

The interview included two coding problems: 1. **Add numbers from character arrays** - You are given two non-empty character arrays, where each array represents a non-negative integer in decimal form. - Each element is a digit character such as `'0'` through `'9'`. - Return the sum as a string. - You may not convert the entire input directly into a built-in integer type. Example: - Input: `['1','2','3']`, `['9','9']` - Output: `"222"` 2. **Evaluate a basic arithmetic expression** - You are given a string expression containing non-negative integers, spaces, and the operators `+`, `-`, `*`, and `/`. - Evaluate the expression and return the integer result. - Operator precedence should be respected: multiplication and division before addition and subtraction. - Integer division truncates toward zero. - The expression is guaranteed to be valid and contains no parentheses. Example: - Input: `"3+2*2"` - Output: `7` - Input: `" 14-3/2 "` - Output: `13`

Quick Answer: This question evaluates string manipulation and parsing skills for numeric computation, covering addition of integers represented as character arrays and correct evaluation of arithmetic expressions with operator precedence.

Part 1: Add Two Numbers from Character Arrays

You are given two non-empty arrays of digit characters. Each array represents a non-negative integer in decimal form, with one digit per element. Return their sum as a string. You may not convert the entire array directly into a built-in integer type or use big integer libraries. Instead, simulate addition the same way you would do it by hand from right to left.

Constraints

1 <= len(digits1), len(digits2) <= 100000
Each element of digits1 and digits2 is a character from '0' to '9'
The input numbers have no leading zeros unless the number itself is zero
You must not convert the entire input into a built-in integer type

Examples

Input: (['1', '2', '3'], ['9', '9'])

Expected Output: "222"

Explanation: 123 + 99 = 222.

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

Expected Output: "1000"

Explanation: A carry propagates through all digits.

Input: (['0'], ['0'])

Expected Output: "0"

Explanation: Edge case: both numbers are zero.

Input: (['5'], ['5'])

Expected Output: "10"

Explanation: Single-digit addition that creates a new leading digit.

Hints

Start from the last digit of each array and move left, just like grade-school addition.
Keep track of a carry value after adding each pair of digits.

Part 2: Evaluate a Basic Arithmetic Expression

You are given a valid string expression containing non-negative integers, spaces, and the operators '+', '-', '*', and '/'. Evaluate the expression and return the integer result. The expression contains no parentheses. Standard operator precedence must be respected: multiplication and division are performed before addition and subtraction. Division truncates toward zero.

Constraints

1 <= len(expression) <= 100000
The expression contains only digits, spaces, and the operators '+', '-', '*', '/'
The expression is guaranteed to be valid and contains no parentheses
Division by zero will not occur
Integer division must truncate toward zero

Examples

Input: "3+2*2"

Expected Output: 7

Explanation: Multiplication happens first: 2 * 2 = 4, then 3 + 4 = 7.

Input: " 14-3/2 "

Expected Output: 13

Explanation: 3 / 2 truncates toward zero to become 1, so 14 - 1 = 13.

Input: "42"

Expected Output: 42

Explanation: Edge case: the expression is just a single number.

Input: " 3+5 / 2 "

Expected Output: 5

Explanation: 5 / 2 truncates toward zero to 2, so 3 + 2 = 5.

Input: "0-3/2"

Expected Output: -1

Explanation: 3 / 2 becomes 1, so 0 - 1 = -1.

Hints

You do not need a full parser. Process the string left to right while remembering the previous operator.
A stack is a simple way to handle precedence: push numbers for + and -, but immediately combine for * and /.

Quick Overview

This question evaluates string manipulation and parsing skills for numeric computation, covering addition of integers represented as character arrays and correct evaluation of arithmetic expressions with operator precedence.