122. Happy Number

Write a function solve that determines if a number is a happy number (eventually reaches 1 when replaced by the sum of the square of each digit).

Example:
Input: 19
Output: true
Explanation: 1^2 + 9^2 = 82 -> 8^2 + 2^2 = 68 -> 6^2 + 8^2 = 100 -> 1^2 + 0^2 + 0^2 = 1.

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