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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0201_0300.s0202_happy_number;

// #Easy #Top_Interview_Questions #Hash_Table #Math #Two_Pointers #Algorithm_II_Day_21_Others
// #Programming_Skills_I_Day_4_Loop #Level_2_Day_1_Implementation/Simulation
// #2022_06_28_Time_1_ms_(98.59%)_Space_41_MB_(64.25%)

/**
 * 202 - Happy Number\.
 *
 * Easy
 *
 * 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:**
 *
 * **Input:** n = 19
 *
 * **Output:** true
 *
 * **Explanation:**
 *
 * 1² + 9² = 82
 *
 * 8² + 2² = 68
 *
 * 6² + 8² = 100
 *
 * 1² + 0² + 0² = 1 
 *
 * **Example 2:**
 *
 * **Input:** n = 2
 *
 * **Output:** false 
 *
 * **Constraints:**
 *
 * *   1 <= n <= 2³¹ - 1
**/
public class Solution {
    public boolean isHappy(int n) {
        boolean happy;
        int a = n;
        int rem;
        int sum = 0;
        if (a == 1 || a == 7) {
            happy = true;
        } else if (a > 1 && a < 10) {
            happy = false;
        } else {
            while (a != 0) {
                rem = a % 10;
                sum = sum + (rem * rem);
                a = a / 10;
            }
            if (sum != 1) {
                happy = isHappy(sum);
            } else {
                happy = true;
            }
        }
        return happy;
    }
}