# 1946. Largest Number After Mutating Substring

https://leetcode.com/problems/largest-number-after-mutating-substring

## Description

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:**

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

## ac

```java
```
