Happy Number — LeetCode 202 Python Solution

The problem

Write an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits.

Example

Input

n = 19

Output

true

Explanation

12 + 92 = 82

Python solution

class Solution:
    def isHappy(self, n: int) -> bool:
        vis = set()
        while n != 1 and n not in vis:
            vis.add(n)
            x = 0
            while n:
                n, v = divmod(n, 10)
                x += v * v
            n = x
        return n == 1

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 202. Happy Number is filed here because LeetCode tags it Two Pointers, which is the vocabulary this hub collects.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

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