# Largest Number After Mutating Substring solution leetcode Biweekly Contest 57 United States

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 any 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) any substring of `num`.

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:

• `1 <= num.length <= 105`
• `num` consists of only digits `0-9`.
• `change.length == 10`
• `0 <= change[d] <= 9`