Largest Odd Number in String LeetCode solution in C++

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class Solution {
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 public:
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  string largestOddNumber(string num) {
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    // Length of the given string
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    int len = num.size();
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    // We initialize an empty string for the result
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    string res = "";
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    // We start searching digits from the very right to left because we want to
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    // find the first odd digit Which will be the last digit of our biggest odd
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    // number
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    for (int i = len - 1; i >= 0; i--) {
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      // Here we just convert char to an integer in C++
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      // We can also do the reverse operation by adding '0' to an int to get
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      // char from an int
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      int isOdd = num[i] - '0';
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      // We check if the current digit is odd, if so this is the position we
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      // want to find
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      if (isOdd % 2 == 1) {
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        // Since we have found the correct spot, let's create our result string
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        // We can basically extract the part starting from 0th index to right
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        // most odd digit's index Like this: 0123456 -> indices 1246878 ->
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        // digits
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        // ^....^ -> The part we extracted [0 to 5]
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        res = num.substr(0, i + 1); // i+1 is length of substring
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        // Because we know this would be the largest substring as we are
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        // starting from last We can terminate the loop and return the result
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        break;
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      }
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    }
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    return res;
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  }
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};