You are given a very large integer n, represented as a string,negative 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 negative. 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 negative after the insertion.

題目給一個非常大的整數n（字串形式表示），還有一個整數x。n和x的每個數字都在1～9的範圍，但n可能是負數！目標是通過將數字x插入到n的十進位表示中來使得n的數值最大化（但不能把x插入到負號左邊）
返回插入後n數值最大化的字串

我的解題思路：

1. 先判斷n的正負
2. 如果n沒有"-"，把X放在n的第一個<=X的數字前
3. 如果n有"-"，把X放在n的第一個>=X的數字後
4. 返回改造後的n

class Solution {
    public String maxValue(String n, int x) {
    
        if (n.charAt(0) == '-') {
            for (int i = 1; i < n.length(); i++) {
                // 如果x小於目前數字，就把x插入
                if (x < n.charAt(i) - '0') {
                    return n.substring(0, i) + x + n.substring(i);
                }
            }
            // x是最大的數字就直接放尾巴
            return n + x;
        }else {
            for (int i = 0; i < n.length(); i++) {
                // 如果x大於目前數字，就把x插入
                if (x > n.charAt(i) - '0') {
                    return n.substring(0, i) + x + n.substring(i);
                }
            }
            // x是最小的數字就直接放尾巴
            return n + x;
        }
    }
}

輕輕鬆鬆！