FirstNonRepeatedCharacter.java

package devjava;

import java.util.LinkedHashMap;
import java.util.Map;

public class FirstNonRepeatedCharacter {

	private static final int EXTENDED_ASCII_CODES = 256;

	public static char firstNonRepeatedCharacter(String str) {
		int[] flags = new int[EXTENDED_ASCII_CODES];

		for (int i = 0; i < flags.length; i++) {
			flags[i] = -1;
		}

		for (int i = 0; i < str.length(); i++) {
			char ch = str.charAt(i);
			if (flags[ch] == -1) {
				flags[ch] = i;
			} else {
				flags[ch] = -2;

			}
		}

		int position = Integer.MAX_VALUE;

		for (int i = 0; i < EXTENDED_ASCII_CODES; i++) {
			if (flags[i] >= 0) {
				position = Math.min(position, flags[i]);
			}
		}
		return position == Integer.MAX_VALUE ? Character.MIN_VALUE : str.charAt(position);
	}

	public static char firstNonRepeatedCharacterMap(String str) {
		Map<Character, Integer> chars = new LinkedHashMap<>();
		for (int i = 0; i < str.length(); i++) {
			char ch = str.charAt(i);
			chars.compute(ch, (k, v) -> (v == null) ? 1 : ++v);
		}
		for (Map.Entry<Character, Integer> entry : chars.entrySet()) {
			if (entry.getValue() == 1) {
				return entry.getKey();
			}
		}
		return Character.MIN_VALUE;
	}

	public static void main(String[] args) {
		System.out.println(firstNonRepeatedCharacterMap("Ananas"));
	}
}