### First non-repeating character in a string character string    Posted: 5 years ago Edit answers (1) views (2867)

Write a function to find the first non-repeating character in a String.

 Posted: 5 years ago Updated: 5 years ago 0 0 Edit Take an empty integer array of $$256$$ elements to hold the frequency of character of the string. Iterate through the string and construct the frequency array. Increment the current value of the frequency array by $$1$$ at the location of the corresponding ASCII value of the character. Iterate through the string and check the frequency array. Return the first element whose frequency is $$1$$. Time complexity = $$O(n)$$.public static char FirstNonRepeatingChar(String string) { /* When the string is null */ if(string == null) throw new NullPointerException(string); /* Create an empty integer array to store the frequency */ int[] charFrequency = new int[256]; /* Construct the frequency array */ for(int i = 0; i < string.length; i++) charFrequency[string.charAt(i)]++; /* Iterate through string and check the frequency */ for(int i = 0; i < string.length; i++){ if(charFrequency[string.charAt(i)] == 1) /* Print the first non repeating character */ return string.charAt(i)); break; } } }