From 9327403a53cf2c7fe30d597aa6ff132421149a35 Mon Sep 17 00:00:00 2001
From: GauravWalia19 <gauravwalia019@gmail.com>
Date: Fri, 25 Jan 2019 21:39:46 +0530
Subject: [PATCH] added dynamic array stack in java

---
 .../DynamicArrayStack.java                    | 182 ++++++++++++++++++
 Java/README.md                                |   1 +
 datastructures.md                             |   6 +
 3 files changed, 189 insertions(+)
 create mode 100644 Java/Data-Structures/STACKS/DYNAMIC-ARRAY-STACK/DynamicArrayStack.java

diff --git a/Java/Data-Structures/STACKS/DYNAMIC-ARRAY-STACK/DynamicArrayStack.java b/Java/Data-Structures/STACKS/DYNAMIC-ARRAY-STACK/DynamicArrayStack.java
new file mode 100644
index 0000000..4e10e3e
--- /dev/null
+++ b/Java/Data-Structures/STACKS/DYNAMIC-ARRAY-STACK/DynamicArrayStack.java
@@ -0,0 +1,182 @@
+import java.util.*;
+abstract class DynamicArrayStack
+{
+    private static class DArrayStack
+    {
+        private int[] stack;            //array for stack
+        private int top;                //top for stack
+        private int s;                  //s for calculating the size of the stack
+
+        /**
+         * DArrayStack()
+         * this is default constructor
+         **/
+        public DArrayStack()
+        {
+            this(1);                    //call parameterised contructor as size 1
+        }
+
+        /**
+         * DArrayStack()
+         * this is parametrized constructor
+         * 
+         * @param num for size of the input 
+         **/
+        public DArrayStack(int num)
+        {
+            this.s = num;
+            top=-1;
+            this.stack = new int[num];
+        }
+
+        /**
+         * push()
+         * this function will push an element to the stack
+         * 
+         * @param num for element to push
+         * 
+         * @return void
+         **/
+        public void push(int num)
+        {
+            if(top==s-1)
+            {
+                expand();               //expand array when stack gets full
+            }            
+            
+            top++;
+            stack[top] = num;           //push to stack
+        }
+
+        /**
+         * expand()
+         * this function will expand the array to its double
+         * 
+         * @param void
+         * 
+         * @return void
+         **/
+        public void expand()
+        {
+            int oldsize = s;
+            s = s*2;                    //increase the array size to double
+            int[] arr = new int[s];
+            for(int i=0;i<oldsize;i++)  //copying current stack to arr
+            {
+                arr[i] = stack[i];
+            }
+            stack = arr;
+        }
+
+        /**
+         * pop()
+         * this function will pop an element from the stack
+         * 
+         * @param none
+         * 
+         * @return int for element to be popped
+         **/
+        public int pop() throws EmptyStackException
+        {
+            if(top==-1)                 //if stack is empty
+            {
+                throw new EmptyStackException();
+            }
+            int temp = stack[top];      
+            stack[top]=0;
+            top--;
+            if(top+1==s/2)
+            {
+                shrink();               //shrink the array size
+            }
+            return temp;
+        }
+
+        /**
+         * shrink()
+         * it will shrink the stack array size to its half
+         * 
+         * @param void
+         * 
+         * @return void
+         **/
+        public void shrink()
+        {
+            s=s/2;
+            int[] arr = new int[s];
+            for(int i=0;i<s;i++)
+            {
+                arr[i] = stack[i];
+            }
+            stack = arr;
+        }
+
+        /**
+         * peek()
+         * it will return the top element of the stack
+         * 
+         * @param void
+         * 
+         * @return int for top element of the stack 
+         **/
+        public int peek()
+        {
+            return stack[top];
+        }
+
+        /**
+         * print()
+         * it will print the whole array for checking only never do that
+         * 
+         * @param void
+         * 
+         * @return void
+         **/
+        public void print()
+        {
+            for(int i=0;i<s;i++)
+            {
+                System.out.print(stack[i]+" ");
+            }
+            System.out.println();
+        }
+
+        /**
+         * size()
+         * it will return the size of the stack
+         * 
+         * @param void
+         * 
+         * @return int for size of the stack
+         **/
+        public int size()
+        {
+            return top+1;
+        }
+    }
+    
+    public static void main(String[] args)
+    {
+        try
+        {
+            DArrayStack S = new DArrayStack();
+            S.push(1);
+            S.push(2);
+            S.push(3);
+            S.push(4);
+            S.push(5);
+            S.push(6);
+            S.push(10);
+            S.pop();
+            S.push(11);
+            S.push(12);
+            S.print();
+            System.out.println(S.peek());
+            System.out.println(S.size());
+        }
+        catch(Exception e)
+        {
+            System.out.println(e);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Java/README.md b/Java/README.md
index cb55b6c..7d7e7d8 100644
--- a/Java/README.md
+++ b/Java/README.md
@@ -53,6 +53,7 @@
 * FIXED ARRAY STACK
   * [FixedArray Stack](Data-Structures/STACKS/FIXED-ARRAY-STACK/ArrayStack.java)
 * DYNAMIC ARRAY STACK
+  * [Dynamic Array Stack](Data-Structures/STACKS/DYNAMIC-ARRAY-STACK/DynamicArrayStack.java)
 * LINKED STACK
   * [Linked Stack](Data-Structures/STACKS/LINKED-STACK/LinkedStack.java)
 * INBUILT STACKS
diff --git a/datastructures.md b/datastructures.md
index ae83f4b..29b8835 100644
--- a/datastructures.md
+++ b/datastructures.md
@@ -196,6 +196,12 @@ Indexer for Data Structures Lover
 
 ### DYNAMIC ARRAY STACK
 
+* blog
+* docs
+* implementation
+  * [JAVA](Java/Data-Structures/STACKS/DYNAMIC-ARRAY-STACK/DynamicArrayStack.java)
+* complexity
+
 ### LINKED STACK
 
 * blog