First Non Recurring Character - HackerRank Solutions

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

Note that 'A' and 'a' are considered as two different characters.

Input Format

A single line containing the input string.

Constraints

3 < L < 10000 => length(string)

Output Format

A single line containing the resulting character.

Sample Input 0

abacabad

Sample Output 0

c

Explanation 0

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

Sample Input 1

abacabaabacaba

Sample Output 1

_

Explanation 1

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

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First Non-Recurring Character - HackerRank Solutions 

#include <stdio.h>  
#include <stdlib.h> 
#define NO_OF_CHARS 256 
int* getCharCountArray(char* str) 
{ 
    int* count = (int*)calloc( 
        sizeof(int), NO_OF_CHARS); 
    int i; 
    for (i = 0; *(str + i); i++) 
        count[*(str + i)]++; 
    return count; 
} 
int firstNonRepeating(char* str) 
{ 
    int* count = getCharCountArray(str); 
    int index = -1, i; 
    for (i = 0; *(str + i); i++) { 
        if (count[*(str + i)] == 1) { 
            index = i; 
            break; 
        } 
    } 
    // To avoid memory leak 
    free(count); 
    return index; 
} 
int main() 
{ 
    char str[10000];
    gets(str);
    int index = firstNonRepeating(str); 
    if (index == -1) 
        printf("_"); 
    else
        printf("%c", str[index]); 
    getchar(); 
    return 0; 
}