Pre-Reqs-Fundamentals-Of-CS-Java

AppendLL.java

package demo.tutorials.demo;

import java.util.List;

/**
 * Created by Preetham on 04/08/18.
 *
 * pseudo code
 *
 * start from head of the linkedlist 1
 * assign next node's ref to head
 * assign list 2 to tail node of linkedlist1 when next node ref is null
 * and repeat till node is not null
 *
 */

class ListNode {
    int dataVal;
    ListNode next;

    public ListNode() {

    }

    public ListNode(int data, ListNode next) {
        this.dataVal = data;
        this.next = next;
    }

    public void appendNode(int data, ListNode next) {
        this.dataVal = data;
        this.next = next;
    }


    public void print() {
        /*ListNode currentNode = this;
        while (currentNode != null) {
            System.out.println(currentNode.dataVal);
            currentNode = currentNode.next;
        }*/
        // short hand way
        for(ListNode currentNode = this;  currentNode!=null; currentNode = currentNode.next){
            System.out.println(currentNode.dataVal);
        }

    }
}

public class AppendLL {

    public static ListNode appendLists(ListNode list1, ListNode list2) {



//        ListNode currNode = list1;
//        while (currNode != null) {
        //
//            if (currNode.next == null) {
//                currNode.next = list2;
//                break;
//            }
//            currNode = currNode.next;
//
//        }

        // smarter version
        for(ListNode currentNode = list1; currentNode != null ; currentNode = currentNode.next){
            if(currentNode.next==null){
                currentNode.next = list2;
                break;
            }
        }
        return list1;
    }

    ;

    public static void main(String[] args) {
        ListNode ll1 = new ListNode();
        ll1.appendNode(1, new ListNode(2, new ListNode(3, null)));
        System.out.println("******* print list 1");
        ll1.print();

        ListNode ll2 = new ListNode(10, new ListNode(11, new ListNode(12, new ListNode(13, null))));
        System.out.println("******* print list 2");
        ll2.print();

        ListNode ll3 = appendLists(ll1, ll2);
        System.out.println("******* print appended list ");
        ll3.print();
    }

}

Diamond.java

package demo.tutorials.demo;

import java.util.Scanner;

/**
 * Created by Preetham on 19/08/18.
 */
public class Diamond {

    private final static String SPACE = " ";
    private final static String STAR = "*";

    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        System.out.print("Please enter the number of rows to be printed: ");
        int rows = scan.nextInt();
        for (int row = 1; row <= rows; row++) {
            int column = row;
            int spaces = rows - column;
            int stars = column;
            // prints one half of pyramid offset with spaces
            //   *
            //  **
            // ***
            for (int space = 1; space <= spaces; space++) {
                System.out.print(SPACE);
            }
            for (int star = 1; star <= stars; star++) {
                System.out.print(STAR);
            }


            // prints the other half starting from second row , first row should contain a single star
            /*
               *
               **
               ***
               ****
            */
            for (int star = 2; star <= stars; star++) {
                System.out.print(STAR);
            }
//               *
//              ***
//             *****
//            *******

            // next line
            System.out.println();
        }
      // reverse the above process
        for (int row = rows; row >= 0; row--) {
            int column = row;
            int spaces = rows - column;
            int stars = column;
            for (int space = spaces; space > 0; space--) {
                System.out.print(SPACE);
            }
            for (int star = stars; star > 0; star--) {
                System.out.print(STAR);
            }
            // should be > or equal to 0 here.
            for (int star = stars - 2; star >= 0; star--) {
                System.out.print(STAR);
            }
            System.out.println();
        }
        //}
    }
}

PrintNthItemArr.java

package demo.tutorials.demo;

import java.util.Scanner;

/**
 * Created by Preetham on 03/08/18.
 */
public class PrintNthItemArr {
    public static void printEveryNthItem(int N, int[] arr){
        for (int index = 0; index < arr.length; index++) {
            // check for multiples
            if (index % N == 0) {
                if (N < arr.length) {
                    System.out.print(arr[index]);
                } else {
                    throw new ArrayIndexOutOfBoundsException();
                }

            }
        }
    };
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.println("Enter the N");
        int N = scan.nextInt();
        int[] arr = new int[]{3, 4, 7, 2, 1, 4, 8, 4, 9, 0, 1, 6};
        printEveryNthItem(N, arr);


    }
}

UpperTriangle.java

package demo.tutorials.demo;

/**
 * Created by Preetham on 31/07/18.
 * Program to print pyramid of stars
 * pseudo code:
 *
 * when rows=5,
 * for row=1 and row less than rows
 * column= row
 * Print second half of pyramid :
 * 	    number of spaces = rows-column
 *      for 'number of spaces' times print a space
 *      for number of  ‘column’ times print star
 * Print first half of pyramid stacking after the second half:
 *       for number of ‘column’ times print a star again , but starting from second row
 * row = row+1
 * print \n
 */
import java.util.Scanner;
public class UpperTriangle {
    private final static String SPACE = " ";
    private final static String STAR = "*";

    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        System.out.print("Please enter the number of rows to be printed: ");
        int rows = scan.nextInt();
        for (int row = 1; row <= rows; row++) {
            int column = row;
            int spaces = rows - column;
            int stars = column;
            // prints one half of pyramid offset with spaces
            //   *
            //  **
            // ***
            for (int space = 1; space <= spaces; space++) {
                System.out.print(SPACE);
            }
            for (int star = 1; star <= stars; star++) {
                System.out.print(STAR);
            }
            // prints the other half starting from second row , first row should contain a single star
            /*
               *
               **
               ***
               ****
            */
            for (int star = 2; star <= stars; star++) {
                System.out.print(STAR);
            }
//               *
//              ***
//             *****
//            *******

            // next line
            System.out.println();
        }
    }
}