Java program to remove duplicate characters from a String with o(n) time complexity

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In our previous post, we have seen one of the very popular java programming interview question"How to balanced parenthesis with o(n) time and space complexity" here.
And in this post again we are going to show you simple java program to remove duplicate characters from a String with o(n) performance. Of course there are lots of way to achieve this and we are using one of them. This type of questions always asked in your coding interview not only for freshers but for experienced candidates also. Sometimes interviewer wants to check your coding skills and he/she may asked you to write a simple program to solve this problem on paper.

UniqueChar.java

package com.javamakeuse.poc;

public class UniqueChar {

	public static String removeDuplicates(String input) {

		// container to hold unique characters
		StringBuilder uniqueChar = new StringBuilder();

		for (int i = 0; i < input.length(); i++) {

			String si = input.substring(i, i + 1);

			if (uniqueChar.indexOf(si) == -1) {
				uniqueChar.append(si);
			}
		}
		return uniqueChar.toString();
	}

	public static void main(String[] args) {
		System.out.println(removeDuplicates("Book"));
		System.out.println(removeDuplicates("Look"));
		System.out.println(removeDuplicates("blaa bla bla"));
	}
}

OUT PUT:
Bok
Lok
bla

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