Happy Number Problem


Description

LeetCode Problem 202.

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.
  • Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
  • Those numbers for which this process ends in 1 are happy.

Return true if n is a happy number, and false if not.

Example 1:

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Input: n = 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

Example 2:

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Input: n = 2
Output: false

Constraints:

  • 1 <= n <= 2^31 - 1


Sample C++ Code

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class Solution {
public:
    bool isHappy(int n) {
        map<int, int> ht;
        int m;
        bool happy = false;
        while (1) {
            ht[n] = 1;
            m = 0;
            while (n > 0) {
                m += (n % 10) * (n % 10);
                n /= 10;
            }
            n = m;
            if (n == 1) {
                happy = true;
                break;
            }
            if (ht.find(n) != ht.end()) {
                happy = false;
                break;
            }
        }
        return happy;
    }
};




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