Merge pull request #819 from kakashi215/main

Create 227_Basic_Calculator_II.py

Python/Basic_Calculator_II.py

@@ -0,0 +1,86 @@
+# Problem link: https://leetcode.com/problems/basic-calculator-ii/
+
+# Implement a basic calculator to evaluate a simple expression string.
+# The expression string contains only non-negative integers and
+# +, -, *, / operators and empty spaces.
+# The integer division should truncate toward zero.
+
+# Example 1:
+#   Input: "3+2*2"
+#   Output: 7
+
+# Example 2:
+#   Input: " 3/2 "
+#   Output: 1
+
+# Example 3:
+#   Input: " 3+5 / 2 "
+#   Output: 5
+
+# Note:
+# You may assume that the given expression is always valid.
+# Do not use the eval built-in library function.
+
+
+"""
+Approach:
+1. Segregate the string into a list with the digits and operations.
+    1.1 Count the operations along the way.
+2. Go through the list twice.
+    2.1 Once to compute all "*" and  "/".
+    2.2 Second to compute all "+" and "-".
+3. Return the final element left in the expression.
+"""
+
+
+class Solution:
+    def segregate(self, s):
+        result = list()
+        operator_count = {"+": 0, "-": 0, "*": 0, "/": 0}
+        item = ""
+        for index, char in enumerate(s):
+            if char.isspace():
+                if item != "":
+                    result.append(int(item))
+                    item = ""
+            if char in ["+", "-", "*", "/"]:
+                operator_count[char] += 1
+                if item != "":
+                    result.append(int(item))
+                    item = ""
+                result.append(char)
+            if char.isnumeric():
+                item += char
+        if item != "":
+            result.append(int(item))
+        return result, operator_count
+
+    def calculate(self, s: str) -> int:
+        exp, operator_count = self.segregate(s)
+        # print("Initial", exp)
+        # print(operator_count)
+        ops = {
+            "+": (lambda x, y: x + y),
+            "-": (lambda x, y: x - y),
+            "*": (lambda x, y: x * y),
+            "/": (lambda x, y: x // y),
+        }
+        index = 0
+        while index < len(exp):
+            if exp[index] in ["/", "*"]:
+                exp[index - 1] = ops[exp[index]](
+                                        exp[index - 1], exp[index + 1])
+                exp.pop(index)
+                exp.pop(index)
+                index -= 1
+            index += 1
+        index = 0
+        while index < len(exp):
+            if exp[index] in ["-", "+"]:
+                exp[index - 1] = ops[exp[index]](
+                                        exp[index - 1], exp[index + 1])
+                exp.pop(index)
+                exp.pop(index)
+                index -= 1
+            index += 1
+        return exp[0]