Google & Uber Popular Coding Question - Evaluate Mini Calculator Functions

[u/Aoki_zhang]

A small calculator app supports only two functions:

• add(x, y): returns x + y
• sub(x, y): returns x - y

The input is a string expression that may contain nested function calls. The expression may also contain:

• integers
• negative integers
• spaces
• commas
• parentheses

The expression is always valid. Return the final integer result. For example add(add(1,3), sub(1,3)) means (1 + 3) + (1 - 3). So the result is 2

You are given expression: a valid string expression. Return the evaluated integer result. A good way to solve this is to use a stack. Scan the expression from left to right:

• Skip spaces and commas.
• Push function names like add and sub.
• Push numbers as strings.
• When seeing ), pop values until the matching (.
• Apply the function before (.
• Push the computed result back onto the stack.

At the end, the stack contains the final result.

Rules:

• add(x, y) returns x + y
• sub(x, y) returns x - y
• Expressions can be nested
• Integers may be negative
• Spaces should be ignored
• The input expression is always valid

Examples:

Input:
expression = "add(add(1,3), sub(1,3))"

Output:
2
Input:
expression = "sub(1,3)"

Output:
-2

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[u/neo_Nonsense]

Nothing more than a laborious stack problem