1946\. Largest Number After Mutating Substring

Medium

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.

**Example 1:**

**Input:** num = "132", change = [9,8,5,0,3,6,4,2,6,8]

**Output:** "832"

**Explanation:** Replace the substring "1": 

- 1 maps to change[1] = 8. Thus, "132" becomes "832". 
  
"832" is the largest number that can be created, so return it.

**Example 2:**

**Input:** num = "021", change = [9,4,3,5,7,2,1,9,0,6]

**Output:** "934"

**Explanation:** Replace the substring "021": 

- 0 maps to change[0] = 9. 

- 2 maps to change[2] = 3. 

- 1 maps to change[1] = 4. 
  
Thus, "021" becomes "934". 

"934" is the largest number that can be created, so return it.

**Example 3:**

**Input:** num = "5", change = [1,4,7,5,3,2,5,6,9,4]

**Output:** "5"

**Explanation:** "5" is already the largest number that can be created, so return it.

**Constraints:**

*   <code>1 <= num.length <= 10<sup>5</sup></code>
*   `num` consists of only digits `0-9`.
*   `change.length == 10`
*   `0 <= change[d] <= 9`