feat: add leetcode75 day33 227

feat: add leetcode75 day33 227

Author: hj.tian

leetcode75/day33_227.py

@@ -0,0 +1,37 @@
+class Solution:
+    def calculate(self, s: str) -> int:
+        """
+        stack: 最后只保留需要相加的数字
+        *: stack[-1] * num
+        /: stack[-1] // num
+        -: -num
+        +: num
+        return sum(stack)
+        """
+        stack = []
+        s = s.strip()
+        num = 0
+        pre_sign = "+"
+        for i in range(len(s)):
+            if s[i].isdigit():
+                num = num * 10 + int(s[i])
+            if s[i] in "+-*/" or i == len(s) - 1:
+                if pre_sign == "+":
+                    stack.append(num)
+                elif pre_sign == "-":
+                    stack.append(-num)
+                elif pre_sign == "*":
+                    stack[-1] = stack[-1] * num
+                elif pre_sign == "/":
+                    # note! -3 // 2 == -2, 所以对负数需要转成正数处理后再变成负数
+                    stack[-1] = stack[-1] // num if stack[-1] > 0 else -((-stack[-1]) // num)
+                num = 0
+                pre_sign = s[i]
+        return sum(stack)
+
+
+if __name__ == "__main__":
+    assert Solution().calculate(s="3+2*2") == 7
+    assert Solution().calculate(s=" 3/2 ") == 1
+    assert Solution().calculate(s=" 3+5 / 2 ") == 5
+    assert Solution().calculate(s="14-3/2") == 13