JavaScript: Find all the possible options to replace the hash in a string

JavaScript Basic: Exercise-116 with Solution

Replace Hash in String to Make Divisible by 3

Write a JavaScript program to find all the possible options to replace the hash in a string (Consists of digits and one hash (#)) with a digit to produce an integer divisible by 3.

For a string "2*0", the output should be : ["210", "240", "270"]

Sample Solution:

JavaScript Code:

// Function to generate strings by replacing '#' in the input with digits making the resulting number divisible by 3
function is_divisible_by3(mask_str) {
  var digitSum = 0, // Variable to hold the sum of digits in the mask string
    left = '0'.charCodeAt(), // ASCII code of '0'
    right = '9'.charCodeAt(), // ASCII code of '9'
    result = [], // Array to store the resulting strings
    mask_data = mask_str.split(''), // Split the input mask string into an array
    hash_pos = -1; // Position of the '#' character

  // Loop through the characters in the mask string array
  for (var i = 0; i < mask_data.length; i++) {
    if (left <= mask_data[i].charCodeAt() && mask_data[i].charCodeAt() <= right) {
      digitSum += mask_data[i].charCodeAt() - left; // Calculate digit sum if character is a digit
    } else {
      hash_pos = i; // Store the position of '#' character
    }
  }

  // Loop through numbers 0 to 9 to replace '#' with digits making the number divisible by 3
  for (var i = 0; i < 10; i++) {
    if ((digitSum + i) % 3 === 0) { // Check if the sum of digits with the new digit is divisible by 3
      mask_data[hash_pos] = String.fromCharCode(left + i); // Replace '#' with the new digit
      result.push(mask_data.join('')); // Push the modified mask string to the result array
    }
  }

  return result; // Return the array containing strings with the '#' replaced by digits
}

// Testing the function with sample inputs
console.log(is_divisible_by3("2#0")); // Output: [ '210', '240', '270' ]
console.log(is_divisible_by3("4#2")); // Output: [ '402', '432', '462', '492' ] 

Output:

["210","240","270"]
["402","432","462","492"]

Live Demo:

See the Pen javascript-basic-exercise-116 by w3resource (@w3resource) on CodePen.

Flowchart:

ES6 Version:

// Function to generate strings by replacing '#' in the input with digits making the resulting number divisible by 3
const is_divisible_by3 = (mask_str) => {
  let digitSum = 0; // Variable to hold the sum of digits in the mask string
  const left = '0'.charCodeAt(); // ASCII code of '0'
  const right = '9'.charCodeAt(); // ASCII code of '9'
  const result = []; // Array to store the resulting strings
  const mask_data = [...mask_str]; // Convert the input mask string to an array
  let hash_pos = -1; // Position of the '#' character

  // Loop through the characters in the mask string array
  for (let i = 0; i < mask_data.length; i++) {
    if (left <= mask_data[i].charCodeAt() && mask_data[i].charCodeAt() <= right) {
      digitSum += mask_data[i].charCodeAt() - left; // Calculate digit sum if character is a digit
    } else {
      hash_pos = i; // Store the position of '#' character
    }
  }

  // Loop through numbers 0 to 9 to replace '#' with digits making the number divisible by 3
  for (let i = 0; i < 10; i++) {
    if ((digitSum + i) % 3 === 0) { // Check if the sum of digits with the new digit is divisible by 3
      mask_data[hash_pos] = String.fromCharCode(left + i); // Replace '#' with the new digit
      result.push(mask_data.join('')); // Push the modified mask string to the result array
    }
  }

  return result; // Return the array containing strings with the '#' replaced by digits
};

// Testing the function with sample inputs
console.log(is_divisible_by3("2#0")); // Output: [ '210', '240', '270' ]
console.log(is_divisible_by3("4#2")); // Output: [ '402', '432', '462', '492' ]

For more Practice: Solve these Related Problems:

• Write a JavaScript program that replaces a hash in a numeric string with digits 0–9 to yield a number divisible by 3.
• Write a JavaScript function that iterates through possible digit replacements for a hash placeholder and returns valid combinations divisible by 3.
• Write a JavaScript program that uses modular arithmetic to test each replacement for a hash in a string and outputs all options yielding divisibility by 3.

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