JavaScript: Find the n^th ugly number

JavaScript Math: Exercise-101 with Solution

Find nth Ugly Number

Write a JavaScript program to find the n^th ugly number.

Ugly numbers are positive numbers whose only prime factors are 2, 3 or 5. The first 10 ugly numbers are:
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, ...
Note: 1 is typically treated as an ugly number.

Visual Presentation:

Test Data:
(4) -> 4
(10) -> 12

Sample Solution:

JavaScript Code:

/**
 * Function to find the nth ugly number.
 * @param {number} num - The number of ugly numbers to find.
 * @returns {number} - The nth ugly number.
 */
function test(num) {
    result = [1]; // Initialize the array with the first ugly number, which is 1
    x2 = x3 = x5 = 0; // Initialize pointers for multiples of 2, 3, and 5
    while (result.length < num) { // Continue until the array contains the specified number of ugly numbers
        m2 = result[x2] * 2; // Calculate the next multiple of 2
        m3 = result[x3] * 3; // Calculate the next multiple of 3
        m5 = result[x5] * 5; // Calculate the next multiple of 5
        temp = Math.min(m2, m3, m5); // Find the smallest among the calculated multiples
        if (temp === m2) { // If the smallest is the multiple of 2, move to the next multiple of 2
            x2++;
        }
        if (temp === m3) { // If the smallest is the multiple of 3, move to the next multiple of 3
            x3++;
        }
        if (temp === m5) { // If the smallest is the multiple of 5, move to the next multiple of 5
            x5++;
        }
        result.push(temp); // Add the smallest ugly number to the result array
    }
    return result[num - 1]; // Return the nth ugly number
};  

// Test cases
n = 4;
console.log("n = " + n);
console.log("nth Ugly number is " + test(n));

n = 10;
console.log("n = " + n);
console.log("nth Ugly number is " + test(n));

Output:

n = 4
nth Ugly number is 4
n = 10
nth Ugly number is 12

Flowchart:

Live Demo:

See the Pen javascript-math-exercise-101 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that uses dynamic programming to generate ugly numbers and finds the nth ugly number.
• Write a JavaScript function that iteratively computes ugly numbers using multiple pointers and returns the nth element.
• Write a JavaScript function that stores computed ugly numbers in an array and retrieves the nth value efficiently.
• Write a JavaScript function that validates the input n and handles edge cases such as non-positive integers.

Go to:

• JavaScript Math and Numbers Exercises Home ↩
• JavaScript Exercises Home ↩

Previous: Check Ugly Number.
NEXT : Count Digit 1 in Range.

Improve this sample solution and post your code through Disqus.