224 Basic Calculator py3

Author: idf

224 Basic Calculator py3.py

@@ -0,0 +1,67 @@
+#!/usr/bin/python3
+"""
+Implement a basic calculator to evaluate a simple expression string.
+
+The expression string may contain open ( and closing parentheses ), the plus +
+or minus sign -, non-negative integers and empty spaces .
+
+Example 1:
+
+Input: "1 + 1"
+Output: 2
+Example 2:
+
+Input: " 2-1 + 2 "
+Output: 3
+Example 3:
+
+Input: "(1+(4+5+2)-3)+(6+8)"
+Output: 23
+Note:
+You may assume that the given expression is always valid.
+Do not use the eval built-in library function.
+"""
+from typing import List
+
+
+class Solution:
+    def calculate(self, s: str) -> int:
+        """
+        1. treat +/- as unary operator
+        2. maintain stk of operands to sum
+        3. handle bracket recursively
+        """
+        ret, _ = self.eval(s + "\0", 0, [])
+        return ret
+
+    def eval(self, s: str, start: int, stk: List[int]) -> int:
+        prev_op = "+"
+        operand = 0
+        i = start
+        while i < len(s):  #  not using for-loop, since the cursor needs to advance in recursion
+            if s[i] == " ":
+                pass
+            elif s[i].isdigit():
+                operand = operand * 10 + int(s[i])
+            elif s[i] in ("+", "-", ")", "\0"):  # delimited
+                if prev_op == "+":
+                    stk.append(operand)
+                elif prev_op == "-":
+                    stk.append(-operand)
+        
+                if s[i] in ("+", "-"):
+                    operand = 0
+                    prev_op = s[i]
+                elif s[i] in (")", "\0"):
+                    return sum(stk), i
+            elif s[i] == "(":
+                # avoid setting operand to 0
+                operand, i = self.eval(s, i + 1, [])
+            else:
+                raise
+
+            i += 1
+
+
+if __name__ == "__main__":
+    assert Solution().calculate("(1+(4+5+2)-3)+(6+8)") == 23

772 Basic Calculator III.py

@@ -30,20 +30,21 @@ def calculate(self, s: str) -> int:
         """
         s = s + "\0"  # signal the end
         ret, _ = self.eval(s, 0, [])
-        print(ret)
         return ret
 
     def eval(self, s, i, stk):
+        """
+        return the cursor since the cursor advances in recursion
+        """
         operand = 0
         prev_op = "+"
         while i < len(s):
             c = s[i]
             if c == " ":
-                i += 1
+                pass  # not continue since need trigger i += 1
             elif c.isdigit():
                 operand = operand * 10 + int(c)
-                i += 1
-            elif c in ("+", "-", "*", "/", ")", "\0"):   # delimited
+            elif c in ("+", "-", "*", "/", ")", "\0"):   # delimiter
                 if prev_op == "+":
                     stk.append(operand)
                 elif prev_op == "-":
@@ -55,22 +56,19 @@ def eval(self, s, i, stk):
                     prev_operand = stk.pop()
                     stk.append(int(prev_operand / operand))
 
-                operand = 0
-                prev_op = c
-                i += 1
-
-                if c == ")":
+                if c in ("+", "-", "*", "/"):
+                    operand = 0
+                    prev_op = c
+                elif c in (")", "\0"):
                     return sum(stk), i
-
-            elif c == "(":
+            elif c == "(":  # "(" is not delimiter
                 operand, i = self.eval(s, i + 1, [])
-            # elif c == ")":
-            #     return sum(stk), i + 1
             else:
                 raise
 
-        return sum(stk), i
+            i += 1
 
 
 if __name__ == "__main__":
+    assert Solution().calculate("(( ( ( 4- 2)+ ( 6+ 10 ) )+ 1) /( ( ( 7 + 9 )* ( 5*8) )- ( 5 + ( 2 * 10 ) ) ) )") == 0
     assert Solution().calculate("(2+6* 3+5- (3*14/7+2)*5)+3") == -12