# 1946. 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

## Solutions

• class Solution {
public String maximumNumber(String num, int[] change) {
char[] s = num.toCharArray();
for (int i = 0; i < s.length; ++i) {
if (change[s[i] - '0'] > s[i] - '0') {
for (; i < s.length && s[i] - '0' <= change[s[i] - '0']; ++i) {
s[i] = (char) (change[s[i] - '0'] + '0');
}
break;
}
}
return String.valueOf(s);
}
}

• class Solution {
public:
string maximumNumber(string num, vector<int>& change) {
int n = num.size();
for (int i = 0; i < n; ++i) {
if (change[num[i] - '0'] > num[i] - '0') {
for (; i < n && change[num[i] - '0'] >= num[i] - '0'; ++i) {
num[i] = change[num[i] - '0'] + '0';
}
break;
}
}
return num;
}
};

• class Solution:
def maximumNumber(self, num: str, change: List[int]) -> str:
s = list(num)
for i, c in enumerate(s):
if change[int(c)] > int(c):
while i < len(s) and int(s[i]) <= change[int(s[i])]:
s[i] = str(change[int(s[i])])
i += 1
break
return ''.join(s)


• func maximumNumber(num string, change []int) string {
s := []byte(num)
for i, c := range num {
if change[c-'0'] > int(c-'0') {
for ; i < len(s) && change[s[i]-'0'] >= int(s[i]-'0'); i++ {
s[i] = byte(change[s[i]-'0']) + '0'
}
break
}
}
return string(s)
}