Stack Implementation added.

Author: sushant097

Stack/StackRecursion.py

@@ -0,0 +1,67 @@
+# Python program to reverse a 
+# stack using recursion
+
+# Recursive funtion that
+# inserts an element
+# at the bottom of a stack.
+def insertAtBottom(stack, item):
+    if isEmpty(stack):
+        push(stack, item)
+    else:
+        value = pop(stack)
+        insertAtBottom(stack, item)
+        push(stack, value)
+
+# Below is the function that
+# reverses the given stack
+# using insertAtBottom()
+def reverse(stack):
+    if not isEmpty(stack):
+        value = pop(stack)
+        reverse(stack)
+        insertAtBottom(stack, value)
+
+# Function to create a stack.
+# It initializes size of a stack as 0
+def createStack():
+    stack = []
+    return stack
+
+# Function to check if
+# the stack is empty
+def isEmpty(stack):
+    return len(stack) == 0
+
+# Function to push an
+# item to stack
+def push(stack, item):
+    stack.append(item)
+
+# Function to pop an 
+# item from stack
+def pop(stack):
+    # if stack is empty
+    # then error
+    if(isEmpty(stack)):
+        print("Stack Underflow!")
+        exit(1)
+    
+    return stack.pop()
+
+# Function to print the stack
+def prints(stack):
+    for i in range(len(stack) - 1, -1, -1):
+        print(stack[i], end = ' ')
+
+stack = createStack()
+push( stack, str(4) )
+push( stack, str(3) )
+push( stack, str(2) )
+push( stack, str(1) )
+print("Original Stack ")
+prints(stack)
+  
+reverse(stack)
+  
+print("Reversed Stack \n")
+prints(stack)