Find first non-repeating character from a String

Carvia Tech | August 05, 2019 | 1 min read | 14 views


Approach

  1. Use a LinkedHashmap to store frequency map of each character. LinkedHashmap keeps the items in the order of their insertion.

  2. Iterate over all the input String one character at a time.

  3. Filter only those entries that have frequency as 1.

  4. Find the fist entry and get its key. This character has not been repeated from given input.

import java.util.LinkedHashMap;
import java.util.Optional;
import java.util.stream.Collectors;

import static java.util.function.Function.identity;

public class Utils {

    private Optional<Character> findFirstNonRepeatingLetter(String s) {
        final Optional<Character> optionalCharacter = s.chars()
                .mapToObj(i -> (char) i)
                .collect(Collectors.groupingBy(identity(), LinkedHashMap::new, Collectors.counting()))
                .entrySet().stream()
                .filter(entry -> entry.getValue() == 1L)
                .map(entry -> entry.getKey())
                .findFirst();
        return optionalCharacter;
    }
}

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