Create design-an-expression-tree-with-evaluate-function.py

Author: kamyu104

Python/design-an-expression-tree-with-evaluate-function.py

@@ -0,0 +1,96 @@
+# Time:  O(n)
+# Space: O(h)
+
+import abc 
+from abc import ABCMeta, abstractmethod 
+
+
+class Node:
+    __metaclass__ = ABCMeta
+    # define your fields here
+    @abstractmethod
+    def evaluate(self):
+        pass
+
+
+import operator
+
+
+class NodeIter(Node):
+    ops = {'+':operator.add, '-':operator.sub, '*':operator.mul, '/':operator.div}
+    
+    def __init__(self, val):
+        self.val = val
+        self.left = None 
+        self.right = None
+    
+    def evaluate(self):
+        result = [0]
+        stk = [(1, (self, result))]
+        while stk:
+            step, args = stk.pop()
+            if step == 1:
+                node, ret = args
+                if node.val.isdigit():
+                    ret[0] = int(node.val)
+                    continue
+                ret1, ret2 = [0], [0]
+                stk.append((2, (node, ret1, ret2, ret)))
+                stk.append((1, (node.right, ret2)))
+                stk.append((1, (node.left, ret1)))
+            elif step == 2:
+                node, ret1, ret2, ret = args
+                ret[0] = NodeIter.ops[node.val](ret1[0], ret2[0])
+        return result[0]
+
+
+class TreeBuilder(object):
+    def buildTree(self, postfix):
+        """
+        :type s: List[str]
+        :rtype: int
+        """
+        stk = []
+        for c in postfix:
+            if c.isdigit():
+                stk.append(NodeIter(c))
+            else:
+                node = NodeIter(c)
+                node.right = stk.pop()
+                node.left = stk.pop()
+                stk.append(node)                
+        return stk.pop()
+
+
+# Time:  O(n)
+# Space: O(h)
+class NodeRecu(Node):
+    ops = {'+':operator.add, '-':operator.sub, '*':operator.mul, '/':operator.div}
+    
+    def __init__(self, val):
+        self.val = val
+        self.left = None 
+        self.right = None
+
+    def evaluate(self):
+        if self.val.isdigit():
+            return int(self.val)
+        return NodeRecu.ops[self.val](self.left.evaluate(), self.right.evaluate())
+        
+
+class TreeBuilder2(object):
+    def buildTree(self, postfix):
+        """
+        :type s: List[str]
+        :rtype: int
+        """
+        stk = []
+        for c in postfix:
+            if c.isdigit():
+                stk.append(NodeRecu(c))
+            else:
+                node = NodeRecu(c)
+                node.right = stk.pop()
+                node.left = stk.pop()
+                stk.append(node)
+        return stk.pop()