LargestNumberAfterMutatingSubstring.cpp

// Source : https://leetcode.com/problems/largest-number-after-mutating-substring/
// Author : Hao Chen
// Date   : 2021-11-12

/***************************************************************************************************** 
 *
 * 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 <= 10^5
 * 	num consists of only digits 0-9.
 * 	change.length == 10
 * 	0 <= change[d] <= 9
 ******************************************************************************************************/

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