Concise O(1) space solution.


  • 0
    U
    public boolean isHappy(int n) {
        if(1 <= n && n <= 9){
            return n == 1 || n == 7;
        }
        int num = 0;
        while(n != 0){
            num += Math.pow(n%10, 2);
            n /= 10;
        }
        return isHappy(num);
    }

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