Checking Oddish and Evenish numbers - JavaScript

A number is Oddish if the sum of all of its digits is odd, and a number is Evenish if the sum of all of its digits is even.

We need to write a function that determines whether a number is Oddish or Evenish. The function should return true for Oddish values and false for Evenish values.

How It Works

The algorithm extracts each digit from the number, adds them up, and checks if the sum is odd or even:

• Extract digits using modulo (num % 10) and integer division (Math.floor(num / 10))
• Sum all digits recursively
• Return true if sum is odd, false if even

Example

const num = 434667;

const isOddish = (num, sum = 0) => {
    if (num) {
        return isOddish(Math.floor(num / 10), sum + (num % 10));
    }
    return sum % 2 === 1;
};

console.log(`Number: ${num}`);
console.log(`Is Oddish: ${isOddish(num)}`);

// Let's trace the digit sum for clarity
let testNum = 434667;
let digits = [];
let temp = testNum;
while (temp > 0) {
    digits.push(temp % 10);
    temp = Math.floor(temp / 10);
}
console.log(`Digits: ${digits.reverse().join(' + ')}`);
console.log(`Sum: ${digits.reduce((a, b) => a + b)}`);

Number: 434667
Is Oddish: false
Digits: 4 + 3 + 4 + 6 + 6 + 7
Sum: 30

Testing Different Numbers

const testNumbers = [123, 456, 789, 111];

testNumbers.forEach(num => {
    console.log(`${num} is ${isOddish(num) ? 'Oddish' : 'Evenish'}`);
});

123 is Evenish
456 is Oddish
789 is Evenish
111 is Oddish

Alternative Implementation

Here's a simpler iterative approach:

const isOddishSimple = (num) => {
    let sum = 0;
    while (num > 0) {
        sum += num % 10;
        num = Math.floor(num / 10);
    }
    return sum % 2 === 1;
};

console.log(isOddishSimple(434667)); // false
console.log(isOddishSimple(123));    // false (1+2+3=6, even)
console.log(isOddishSimple(789));    // false (7+8+9=24, even)
console.log(isOddishSimple(111));    // true (1+1+1=3, odd)

false
false
false
true

Conclusion

Both recursive and iterative approaches work effectively for determining Oddish vs Evenish numbers. The key is summing all digits and checking if the result is odd or even.