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MyStack.java
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211 lines (196 loc) · 4.54 KB
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/*/stack using arraylist.............
import java.util.ArrayList;
public class Stack {
static ArrayList<Integer>list=new ArrayList<>();
public static boolean isEmpty(){
return list.size()==0;
}
//push
public static void push(int data){
list.add(data);
}
//pop
public static int pop(){
if(isEmpty()){
return -1;
}
int top=list.get(list.size()-1);
list.remove(list.size()-1);
return top;
}
//peek
public static int peek(){
if(isEmpty()){
return -1;
}
return list.get(list.size()-1);
}
public static void main(String[] args) {
Stack s=new Stack();
s.push(1);
s.push(2);
s.push(3);
while(!s.isEmpty()){
System.out.println(s.peek());
s.pop();
}
}
}
*/
/*/stack using linkedlist..........
public class Stack {
static class Node{
int data;
Node next;
Node(int data){
this.data=data;
this.next=null;
}
}
static class stack{
static Node head=null;
public static boolean isEmpty(){
return head==null;
}
//push
public static void push(int data){
Node newNode=new Node(data);
if(isEmpty()){
head=newNode;
return;
}
newNode.next=head;
head=newNode;
}
//pop
public static int pop(){
if(isEmpty()){
return -1;
}
int top=head.data;
head=head.next;
return top;
}
//peek
public static int peek(){
if(isEmpty()){
return -1;
}
return head.data;
}
}
public static void main(String[] args) {
stack s=new stack();
s.push(1);
s.push(2);
s.push(3);
while(!s.isEmpty()){
System.out.println(s.peek());
s.pop();
}
}
}
*/
/*/stack java collection framework
import java.util.*;
public class MyStack {
public static void main(String[] args) {
Stack<Integer> s = new Stack<>();
s.push(1);
s.push(2);
s.push(3);
while(!s.isEmpty()){
System.out.println(s.peek());
s.pop();
}
}
}
*/
/*/push at Bottam in stack
import java.util.*;
public class MyStack {
public static void pushAtBottom(Stack<Integer> s, int data) {
if (s.isEmpty()) {
s.push(data);
return;
}
int top = s.pop();
pushAtBottom(s, data);
s.push(top);
}
public static void main(String[] args) {
Stack<Integer> s = new Stack<>();
s.push(1);
s.push(2);
s.push(3);
pushAtBottom(s, 4); // 4 को bottom पर डालेंगे
while (!s.isEmpty()) {
System.out.println(s.peek());
s.pop();
}
}
}
*/
/*/reverse a string using stack
import java.util.*;
public class MyStack {
public static String reverseString(String str){
Stack <Character> s= new Stack<>();
int idx=0;
while(idx<str.length()){
s.push(str.charAt(idx));
idx++;
}
StringBuilder result= new StringBuilder(" ");
while(!s.isEmpty()){
char curr= s.pop();
result.append(curr);
}
return result.toString();
}
public static void main(String[] args) {
String str="abc";
String result = reverseString(str);
System.out.println(result);
}
}
*/
/*/reverse stack....
import java.util.*;
public class MyStack {
public static void pushAtBottom(Stack<Integer> s, int data) {
if (s.isEmpty()) {
s.push(data);
return;
}
int top = s.pop();
pushAtBottom(s, data);
s.push(top);
}
public static void reverseStack(Stack <Integer>s){
if(s.isEmpty()){
return;
}
int top=s.pop();
reverseStack(s);
pushAtBottom(s, top);
}
public static void printStack(Stack <Integer>s){
while(!s.isEmpty()){
System.out.println(s.pop());
}
}
public static void main(String[] args) {
Stack <Integer> s= new Stack<>();
s.push(1);
s.push(2);
s.push(3);
//3,2,1
reverseStack(s);
printStack(s);
//1,2,3
}
}
*/
public class MyStack {
}