JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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Program: Find longest substring without repeating characters.


Description:

Given a string, find the longest substrings without repeating characters. Iterate through the given string, find the longest maximum substrings.


Code:
package com.java2novice.algos;

import java.util.HashSet;
import java.util.Set;

public class MyLongestSubstr {

	private Set<String> subStrList = new HashSet<String>();
	private int finalSubStrSize = 0;
	
	public Set<String> getLongestSubstr(String input){
		//reset instance variables
		subStrList.clear();
		finalSubStrSize = 0;
		// have a boolean flag on each character ascii value
		boolean[] flag = new boolean[256];
		int j = 0;
		char[] inputCharArr = input.toCharArray();
		for (int i = 0; i < inputCharArr.length; i++) {
			char c = inputCharArr[i];
			if (flag[c]) {
				extractSubString(inputCharArr,j,i);
				for (int k = j; k < i; k++) {
					if (inputCharArr[k] == c) {
						j = k + 1;
						break;
					}
					flag[inputCharArr[k]] = false;
				}	
			} else {
				flag[c] = true;
			}
		}
		extractSubString(inputCharArr,j,inputCharArr.length);
		return subStrList;
	}
	
	private String extractSubString(char[] inputArr, int start, int end){
		
		StringBuilder sb = new StringBuilder();
		for(int i=start;i<end;i++){
			sb.append(inputArr[i]);
		}
		String subStr = sb.toString();
		if(subStr.length() > finalSubStrSize){
			finalSubStrSize = subStr.length();
			subStrList.clear();
			subStrList.add(subStr);
		} else if(subStr.length() == finalSubStrSize){
			subStrList.add(subStr);
		}
		
		return sb.toString();
	}

	public static void main(String a[]){
		MyLongestSubstr mls = new MyLongestSubstr();
		System.out.println(mls.getLongestSubstr("java2novice"));
		System.out.println(mls.getLongestSubstr("java_language_is_sweet"));
		System.out.println(mls.getLongestSubstr("java_java_java_java"));
		System.out.println(mls.getLongestSubstr("abcabcbb"));
	}
}

Output:
[a2novice]
[uage_is]
[_jav, va_j]
[cab, abc, bca]
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  30. Write a program to find two lines with max characters in descending order.
  31. Write a program to find the sum of the first 1000 prime numbers.
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Knowledge Centre
What is wrapper class?
Everything in java is an object, except primitives. Primitives are int, short, long, boolean, etc. Since they are not objects, they cannot return as objects, and collection of objects. To support this, java provides wrapper classes to move primitives to objects. Some of the wrapper classes are Integer, Long, Boolean, etc.
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected] or you can comment on the page.

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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