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Commit b169cda

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added leetcode questions
1 parent 958f350 commit b169cda

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3 files changed

+213
-0
lines changed

3 files changed

+213
-0
lines changed
Lines changed: 165 additions & 0 deletions
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package DSA_College.DoublyLinkedList;
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public class DoublyLinkedList {
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ListNode head;
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ListNode tail;
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int size = 0;
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DoublyLinkedList() {
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this.head = null;
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this.tail = null;
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this.size = 0;
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}
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// ListNode class
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private static class ListNode {
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int data;
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ListNode prev;
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ListNode next;
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ListNode(int data) {
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this.data = data;
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this.prev = null;
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this.next = null;
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}
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}
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// add node at start
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public void insertFirst(int data) {
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ListNode node = new ListNode(data);
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if (head == null) {
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head = node;
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node.next = null;
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tail = node;
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} else {
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node.next = head;
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node.prev = null;
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head = node;
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}
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size ++;
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}
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// insert at index
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public void insert(int index, int data) {
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ListNode node = new ListNode(data);
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if (head == null) {
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insertFirst(data);
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} else {
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ListNode n = head;
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int i = 0;
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while (i < index - 1) {
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n = n.next;
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i ++;
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}
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node.next = n.next;
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n.next.prev = node;
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n.next = node;
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node.prev = n;
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}
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size ++;
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}
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// insert at last
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public void insertLast(int data) {
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ListNode node = new ListNode(data);
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if (head == null) {
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insertFirst(data);
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} else {
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node.prev = tail;
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tail.next = node;
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node.next = null;
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tail = node;
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size++;
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}
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}
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// returns size of the linked list
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public int size() {
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return size;
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}
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// method to check is linked list empty or not
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public boolean isEmpty() {
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return size == 0;
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}
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// display forward
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public void displayForward() {
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ListNode n = head;
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while (n != null) {
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System.out.print(n.data + " -> ");
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n = n.next;
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}
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System.out.println("null");
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}
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// display backward
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public void displayBackward() {
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ListNode n = tail;
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while (n != null) {
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System.out.print(n.data + " -> ");
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n = n.prev;
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}
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System.out.println("null");
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}
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// delete at first
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public int deleteFirst() {
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if (isEmpty()) {
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System.out.println("List is Empty");
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return -1;
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}
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if (head == tail) {
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int data = head.data;
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head = tail = null;
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return data;
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}
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int data = head.data;
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head = head.next;
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head.prev = null;
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return data;
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}
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// delete last
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public int deleteLast() {
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if (isEmpty()) {
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System.out.println("List is Empty");
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return -1;
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}
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if (head == tail) {
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int data = head.data;
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head = tail = null;
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return data;
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}
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int data = tail.data;
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tail = tail.next;
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tail.prev = null;
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return data;
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}
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public static void main(String[] args) {
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DoublyLinkedList dll = new DoublyLinkedList();
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dll.insertFirst(10);
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dll.insertFirst(20);
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dll.insertFirst(30);
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dll.displayForward();
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System.out.println(dll.size());
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dll.insertLast(5);
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dll.displayForward();
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System.out.println(dll.size());
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dll.insert(2, 25);
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dll.displayForward();
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System.out.println(dll.size());
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dll.displayBackward();
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System.out.println();
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dll.displayForward();
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System.out.println("Deleted Node => " + dll.deleteFirst());
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dll.displayForward();
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System.out.println(dll.size());
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}
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}

‎Leetcode/Leetcode_231.java

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package Leetcode;
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public class Leetcode_231 {
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// iterative approach
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// public boolean isPowerOfTwo(int n) {
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// if (n <= 0)
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// return false;
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// while(n > 1) {
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// if (n % 2 != 0)
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// return false;
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// n = n / 2;
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// }
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// return true;
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// }
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// bitwise approach
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// public static boolean isPowerOfTwo(int n) {
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// int a = Integer.bitCount(n);
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// return a == 1;
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//
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// }
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// bitwise approach 2
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public static boolean isPowerOfTwo(int n) {
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if (n == 0)
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return false;
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return ((long) n & ((long) n - 1)) == 0;
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}
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public static void main(String[] args) {
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System.out.println(isPowerOfTwo(28));
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}
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}

‎Leetcode/Leetcode_392.java

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package Leetcode;
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//public class Leetcode_392 {
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// public boolean isSubsequence(String s, String t) {
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// if (s.equals(t) || s.isEmpty())
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// return true;
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// if (t.length() < s.length())
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// return false;
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// int j, i;
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// i = j = 0;
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// for (int i1 = 0; i1 < t.length(); i1++) {
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//
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// }
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// }
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//}

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