Basic Calculator Ii

0227.Basic-Calculator-II/memo.md

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+# 227. Basic Calculator II
+
+## step1
+とりあえず答えを合わせるために書き上げたもの: step1。これでも文法ミスなどで25mほどかかった。
+
+確認: // -> 常に小さい方向に丸める, int(・ / ・) -> 小数点以下を切り捨て
+
+## 他の人のコード
+
+https://leetcode.com/problems/basic-calculator-ii/solutions/7632696/a-simple-solution-by-santhanapandis-5vtt/
+
+最後に番兵として "+" を足す
+
+https://github.com/potrue/leetcode/pull/64
+
+## step2
+
+無駄が多いので書き直す。一巡目で+-も処理できる。
+
+さらに例外処理を追加。
+
+再帰下構文解析で書く。
+
+空ではかけず以下の自分の解法を見ながら書いた。
+
+https://leetcode.com/problems/basic-calculator/description/
+
+
+以下の文法に従う
+
+```
+expr   := term  [ ('+' or '-')  term ]*
+term   := factor [ ('*' or '/') factor ]*
+factor := digit+
+```
+
+## step3
+
+再帰下構文解析を練習する

0227.Basic-Calculator-II/step1.py

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+class Solution:
+    def calculate(self, s: str) -> int:
+        def parse_number(left):
+            number = 0
+            right = left
+            while right < len(s) and s[right].isdigit():
+                right += 1
+
+            return s[left:right], right
+
+        operator_to_func = {
+            "*": lambda ops: ops[0] * ops[1],
+            "/": lambda ops: ops[0] // ops[1],
+        }
+
+        to_be_calculated = []
+        i = 0
+        result = 0
+        sign = 1
+        while i < len(s):
+            if s[i] == " ":
+                i += 1
+            elif s[i].isdigit():
+                number, i = parse_number(i)
+                to_be_calculated.append(number)
+            elif s[i] in ["*", "/"]:
+                operator = s[i]
+                op1 = to_be_calculated.pop()
+                i += 1
+                while s[i] == " ":
+                    i += 1
+                assert s[i].isdigit(), s[i]
+                op2, i = parse_number(i)
+                number = operator_to_func[operator]((int(op1), int(op2)))
+                to_be_calculated.append(str(number))
+            elif s[i] in ["+", "-"]:
+                to_be_calculated.append(s[i])
+                i += 1
+            else:
+                raise RuntimeError("invalid input")
+
+        result = 0
+        sign = 1
+        number = 0
+        i = 0
+        print(to_be_calculated)
+        while i < len(to_be_calculated):
+            if to_be_calculated[i].isdigit():
+                result += int(to_be_calculated[i]) * sign
+                i += 1
+            elif to_be_calculated[i] == "+":
+                sign = 1
+                i += 1
+            elif to_be_calculated[i] == "-":
+                sign = -1
+                i += 1
+            else:
+                raise RuntimeError("invalid input")
+
+        return result

0227.Basic-Calculator-II/step2.py

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+class Solution:
+    def calculate(self, s: str) -> int:
+        stack = []
+        number = 0
+        op = "+"
+
+        i = 0
+        while i < len(s):
+            if s[i].isdigit():
+                number = number * 10 + int(s[i])
+
+            if s[i] in ["+", "-", "*", "/"] or i == len(s):
+                if op == "+":
+                    stack.append(number)
+                elif op == "-":
+                    stack.append(-number)
+                elif op == "*":
+                    stack.append(stack.pop() * number)
+                elif op == "/":
+                    stack.append(int(stack.pop() / number))
+                op = s[i]
+                number = 0
+
+            i += 1
+
+        return sum(stack)

0227.Basic-Calculator-II/step2_error_handling.py

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+class Solution:
+    def calculate(self, s: str) -> int:
+        stack = []
+        number = 0
+        op = "+"
+
+        i = 0
+        expect_number = True
+
+        while i < len(s):
+            if i != len(s) - 1 and s[i] == " ":
+                i += 1
+                continue
+            elif s[i].isdigit():
+                number = number * 10 + int(s[i])
+                expect_number = False
+            elif expect_number or s[i] not in ["+", "-", "*", "/", " "]:
+                raise ValueError(f"invalid input: {s[i]}")
+
+            if s[i] in ["+", "-", "*", "/"] or i == len(s) - 1:
+                if op == "+":
+                    stack.append(number)
+                elif op == "-":
+                    stack.append(-number)
+                elif op == "*":
+                    stack.append(stack.pop() * number)
+                elif op == "/":
+                    if number == 0:
+                        raise ZeroDivisionError("Division by zero")
+                    stack.append(int(stack.pop() / number))
+                op = s[i]
+                number = 0
+                expect_number = True
+            i += 1
+
+        return sum(stack)

0227.Basic-Calculator-II/step2_parsing.py

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+"""
+expr   := term  [ ('+' or '-')  term ]*
+term   := factor [ ('*' or '/') factor ]*
+factor := digit+
+"""
+
+
+class Solution:
+    def calculate(self, s: str) -> int:
+        s = s.replace(" ", "")
+        index = 0
+
+        def expr():
+            nonlocal index
+            result = term()
+            while index < len(s) and s[index] in ["+", "-"]:
+                op = s[index]
+                index += 1
+                if op == "+":
+                    result += term()
+                else:
+                    result -= term()
+
+            return result
+
+        def term():
+            nonlocal index
+            result = factor()
+            while index < len(s) and s[index] in ["*", "/"]:
+                op = s[index]
+                index += 1
+                if op == "*":
+                    result *= factor()
+                else:
+                    result = int(result / factor())
+
+            return result
+
+        def factor():
+            nonlocal index
+            result = 0
+            while index < len(s) and s[index].isdigit():
+                result = result * 10 + int(s[index])
+                index += 1
+            return result
+
+        return expr()

0227.Basic-Calculator-II/step3_parsing.py

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+"""
+expr   := term  [ ('+' or '-')  term ]*
+term   := factor [ ('*' or '/') factor ]*
+factor := digit+
+"""
+
+
+class Solution:
+    def calculate(self, s: str) -> int:
+        s = s.replace(" ", "")
+        index = 0
+
+        def expr():
+            nonlocal index
+            result = term()
+            while index < len(s) and s[index] in ("+", "-"):
+                op = s[index]
+                index += 1
+                if op == "+":
+                    result += term()
+                else:
+                    result -= term()
+
+            return result
+
+        def term():
+            nonlocal index
+            result = factor()
+            while index < len(s) and s[index] in ("*", "/"):
+                op = s[index]
+                index += 1
+                if op == "*":
+                    result *= factor()
+                else:
+                    result = int(result / factor())
+
+            return result
+
+        def factor():
+            nonlocal index
+            result = 0
+            while index < len(s) and s[index].isdigit():
+                result = result * 10 + int(s[index])
+                index += 1
+            return result
+
+        return expr()