1881. Maximum Value after Insertion

Problem

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 <= 10^5

• 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 '-'.

Solution (Java)

class Solution {
    public String maxValue(String n, int x) {
        int i = 0;
        int sign = n.charAt(0) == '-' ? -1 : 1;
        for (; i < n.length(); i++) {
            if (n.charAt(i) != '-' && (sign * (n.charAt(i) - '0') < sign * x)) {
                break;
            }
        }
        return n.substring(0, i) + x + n.substring(i);
    }
}

Explain:

nope.

Complexity:

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