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

Solution: Greedy

Find the first digit that is less equal to the mutated one as the start of the substring, keep replacing as long as mutated >= current.

Time complexity: O(n)
Space complexity: O(1)

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

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