Solve String Addition and Expression Evaluation

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`