上传文件至 ''

bee

@@ -0,0 +1,46 @@
+class Stack:  
+    def __init__(self):  
+        self.items = []  
+          
+    def isEmpty(self):  
+        return len(self.items)==0   
+      
+    def push(self, item):  
+        self.items.append(item)  
+      
+    def pop(self):  
+        return self.items.pop()   
+      
+    def peek(self):  
+        if not self.isEmpty():  
+            return self.items[len(self.items)-1]  
+          
+    def size(self):  
+        return len(self.items)
+ 
+   
+def postfixEval(postfixExpr):  
+    operandStack = Stack()  
+    tokenList =postfixExpr.split()  
+   
+    for token in tokenList:  
+        if token in"0123456789":  
+           operandStack.push(int(token))  
+        else:  
+            operand2 =operandStack.pop()  
+            operand1 =operandStack.pop()  
+            result =doMath(token,operand1,operand2)  
+            operandStack.push(result)  
+    return operandStack.pop()  
+   
+def doMath(op, op1, op2):  
+    if op == "*":  
+        return op1 * op2  
+    elif op == "/":  
+        return op1 / op2  
+    elif op == "+":  
+        return op1 + op2  
+    else:  
+        return op1 - op2  
+   
+print(postfixEval('7 8 + 3 2 + /'))