1881. Maximum Value after Insertion

Description

You are given a very large integer n, represented as a string,​​​​​​ and an integer digit x. The digits in n and the digit x are in the inclusive range [1, 9], and n may represent a negative number.

You want to maximize n's numerical value by inserting x anywhere in the decimal representation of n​​​​​​. You cannot insert x to the left of the negative sign.

• For example, if n = 73 and x = 6, it would be best to insert it between 7 and 3, making n = 763.
• If n = -55 and x = 2, it would be best to insert it before the first 5, making n = -255.

Return a string representing the maximum value of n​​​​​​ after the insertion.

 

Example 1:

Input: n = "99", x = 9
Output: "999"
Explanation: The result is the same regardless of where you insert 9.

Example 2:

Input: n = "-13", x = 2
Output: "-123"
Explanation: You can make n one of {-213, -123, -132}, and the largest of those three is -123.

 

Constraints:

• 1 <= n.length <= 105
• 1 <= x <= 9
• The digits in n​​​ are in the range [1, 9].
• n is a valid representation of an integer.
• In the case of a negative n,​​​​​​ it will begin with '-'.

 

Solutions

Solution: Greedy

• Time complexity: O(n)
• Space complexity: O(1)

 

JavaScript

/**
 * @param {string} n
 * @param {number} x
 * @return {string}
 */
const maxValue = function (n, x) {
  const isNegative = Math.sign(n) === -1;
  const start = isNegative ? 1 : 0;

  for (let index = start; index < n.length; index++) {
    const value = n[index];

    if (isNegative && value <= x) continue;
    if (!isNegative && value >= x) continue;
    return `${n.slice(0, index)}${x}${n.slice(index)}`;
  }
  return `${n}${x}`;
};