firstNotRepeatingCharacter.md

First Not Repeating Character

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Given a string s consisting of small English letters, find and return the first instance of a non-repeating character in it. If there is no such character, return '_'.

Example

• For s = "abacabad", the output should be
  solution(s) = 'c'.

  There are 2 non-repeating characters in the string: 'c' and 'd'. Return c since it appears in the string first.

• For s = "abacabaabacaba", the output should be
  solution(s) = '_'.

  There are no characters in this string that do not repeat.

Input/Output

• [execution time limit] 0.5 seconds (cpp)

• [input] string s

  A string that contains only lowercase English letters.

  Guaranteed constraints:
  1 ≤ s.length ≤ 10^5^.

• [output] char

  The first non-repeating character in s, or '_' if there are no characters that do not repeat.

[C++] Syntax Tips

// Prints help message to the console
// Returns a string
string helloWorld(string name) {
    cout << "This prints to the console when you Run Tests" << endl;
    return "Hello, " + name;
}

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Solution

char solution(string s) {
    int counting[26] = {};
    for (int i = 0; i < s.size(); i++) {
        counting[int(s[i]) - 97] ++;
    }
    
    for (int i = 0; i < s.size(); i++) {
        if(counting[int(s[i]) - 97] == 1){
            return s[i];
        }
    }
    
    return '_';
}

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