Given a string s representing a mathematical expression containing non-negative integers and the operators +, -, *, and /, evaluate the expression and return its result.

Integer division must truncate toward zero. You may assume the expression is always valid, and all intermediate results fall within the $32$-bit signed integer range.

Note: Using any built-in function that directly evaluates strings as mathematical expressions (e.g., eval()) is not allowed.

Constraints:

• $1 \leq$ s.length $\leq 3 \times 10^5$

• s consists of non-negative integers and operators ('+', '-', '*', '/') separated by some number of spaces

• s represents a valid expression

• All integers in s are in the range $[0, 2^{31} - 1]$

• The answer is guaranteed to fit within a $32$-bit signed integer

Now, let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.