More Exercises

Longest Substring without repeating characters.

Example 1:

Input: abcabcdbb
Output: abcd

Example 2:

Input: aaaaa
Output: a

Solution:

public class Main {
    public static String longestNonRepeating(String str){
        String temp = "";
        String longest = "";

        for (int i = 0; i < str.length(); i++) {
            char current_char = str.charAt(i);

            //if in string
            //indexOf: Returns -1 if not found
            if (temp.indexOf(current_char) == -1){
                temp += current_char;
            } else { //if in string
                if (temp.length() > longest.length())
                    longest = temp;

                temp = ""; //Reset the string
            }
        }

        return longest.length()>temp.length() ? longest : temp; //Since it temp was always the longest
    }

    public static void main(String[] args) {
        String res = longestNonRepeating("pickoutthelongestsubstring");
        System.out.print("substring: " + res);
        System.out.println(", length: " +res.length());
    }
}

substring: ubstring, length: 8

Tests

import org.junit.jupiter.api.*;
import static org.junit.jupiter.api.Assertions.*;

import static com.company.Main.longestNonRepeating;

public class MyTests {

    @Test
    void TestLongestSubsequence(){
        assertEquals("abc", longestNonRepeating("abcabcbb"));
        assertEquals("b", longestNonRepeating("bbbbb"));

        boolean ifEmpty = longestNonRepeating("").length() == 0;
        assertTrue(ifEmpty);

        String res = longestNonRepeating("pickoutthelongestsubstring");
        assertEquals("ubstring", res);
    }
}

Tests passed: 1 of 1 test

Length of each word

Given a string s containing a string seperated by spaces calculate the length of each word

Example 1:

Input: s = "hello friends"
Output: 5 7

Example 2:

Input: s = "my name is nissan"
Output: 2 4 2 6

Solution

public class Main {
    public static int[] lenOfEachWord(String str){
//       String[] strings = str.split(" ");
       String[] strings = str.split("\\s+");
       int[] lens = new int[strings.length];

        for (int i = 0; i < strings.length; i++)
            lens[i] = strings[i].length();

        return lens;
    }


    public static void main(String[] args) {
        int[] lens = lenOfEachWord("hello  world my name");

        for (int i = 0; i < lens.length; i++)
            System.out.println(lens[i]);
    }
}

Longest substring appears at both ends of a given string

Example 1:

Input: playersplay
Output: play

Example 2:

Input: 1234abc123
Output: 123

Example 2:

Input: helloworld
Output:

Solution

public class Main {
    public static String appearAtBothEnds(String str) {
        int len = str.length();
        String front_and_back_str = "";
        String tmp = "";

        for (int i = 0; i < len; i++) {
            tmp += str.charAt(i);
            int temp_len = tmp.length();

            String sub = str.substring(len-temp_len,len);
            if (i < len / 2 && tmp.equals(sub))
                front_and_back_str = tmp;
        }
        return front_and_back_str;
    }

    public static void main (String[] args) {
        String str =  "playersplay";
        System.out.println("string is: "+str);
        System.out.println("The longest substring is: "+appearAtBothEnds(str));
    }
}

tests

import org.junit.jupiter.api.*;
import static org.junit.jupiter.api.Assertions.*;

import static com.company.Main.appearInBothEnds;

public class MyTests {

    @Test
    void TestAppearAtBothEnds(){
        assertEquals("play", appearAtBothEnds("playersplay"));
        assertEquals("123", appearAtBothEnds("1234abc123"));
        assertEquals("", appearAtBothEnds("helloworld"));
    }
}

Tests passed: 1 of 1 test