199. Convert Binary to Decimal

Write a function solve that takes a string representing a binary number and returns its decimal equivalent as an integer.

Example:
Input: "1010"
Output: 10

Because 1010₂ = 1×8 + 0×4 + 1×2 + 0×1 = 10₁₀

Run this challenge interactively in Python or JavaScript when the app loads.