fixes

src/abstract_structures/adt/stacks/linked_stack.py

@@ -0,0 +1,52 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+class Node:
+    def __init__(self, value=None):
+        self.value = value 
+        self.next = None
+
+class StackwithNodes:
+    ''' Define a Stack with nodes'''
+    def __init__(self):
+        self.top = None
+
+    def isEmpty(self):
+        return bool(self.top)
+
+    def pop(self):
+        node = self.top
+        self.top = node.next
+        return node.value
+
+    def push(self, value):
+        node = Node(value)
+        node.next = self.top
+        self.top = node
+
+    def size(self):
+        node = self.top
+        if node not None: num_nodes = 1
+        else: return 0
+        while node.next:
+            num_nodes += 1
+            node = node.next
+        return num_nodes
+
+    def peek(self):
+        return self.top.value
+        
+        
+def main():
+    stack = StackwithNodes()
+    stack.push(1)
+    stack.push(2)
+    stack.push(3)
+    print(stack.size())    
+    print(stack.peek())   
+    print(stack.pop())  
+    print(stack.peek())    
+
+if __name__ == '__main__':
+    main()