#1946 - Largest Number After Mutating Substring

Problem Description

You are given a string num, which represents a large integer. You are also given a 0-indexed integer array change of length 10 that maps each digit 0-9 to another digit. More formally, digit d maps to digit change[d].

You may choose to mutate a single substring of num. To mutate a substring, replace each digit num[i] with the digit it maps to in change (i.e. replace num[i] with change[num[i]]).

Return a string representing the largest possible integer after mutating (or choosing not to) a single substring of num.

A substring is a contiguous sequence of characters within the string.

Solution

/**
 * @param {string} num
 * @param {number[]} change
 * @return {string}
 */
var maximumNumber = function(num, change) {
  const digits = num.split('');
  let mutated = false;

  for (let i = 0; i < digits.length; i++) {
    const currentDigit = parseInt(digits[i]);
    const mappedDigit = change[currentDigit];

    if (mappedDigit > currentDigit) {
      digits[i] = mappedDigit.toString();
      mutated = true;
    } else if (mappedDigit < currentDigit && mutated) {
      break;
    }
  }

  return digits.join('');
};