diff --git a/grind75_hard/06_224_Basic Calculator/level_1.py b/grind75_hard/06_224_Basic Calculator/level_1.py
new file mode 100644
index 0000000..b83ab54
--- /dev/null
+++ b/grind75_hard/06_224_Basic Calculator/level_1.py	
@@ -0,0 +1,39 @@
+# 数字符号も含め10進数に直して、最後に全部足し算する
+# ()で囲まれた部分を先に計算するため、stackに入れておく
+# 各文字に対する処理をそれぞれ記載
+class Solution:
+    def calculate(self, s: str) -> int:
+        stack = []
+        sign = 1
+        num = 0
+        for c in s:
+            if c.isspace():
+                continue
+            if c.isdigit():
+                num = num * 10 + int(c)
+                continue
+            if c == "(":
+                stack.append((c, sign))
+                sign = 1
+                continue
+            if c == "-":
+                stack.append((num, sign))
+                sign = -1
+            if c == "+":
+                stack.append((num, sign))
+                sign = 1
+            if c == ")":
+                num *= sign
+                while 1:
+                    expression, sign = stack.pop()
+                    if expression == "(":
+                        break
+                    num += expression * sign
+                stack.append((num, sign))
+            num = 0
+        if num != 0:
+            stack.append((num, sign))
+        result = 0
+        for num, sign in stack:
+            result += num * sign
+        return result
diff --git a/grind75_hard/06_224_Basic Calculator/level_2.py b/grind75_hard/06_224_Basic Calculator/level_2.py
new file mode 100644
index 0000000..b8461c9
--- /dev/null
+++ b/grind75_hard/06_224_Basic Calculator/level_2.py	
@@ -0,0 +1,29 @@
+# 括弧内の計算を再帰的に行う
+class Solution:
+    def calculate(self, s: str) -> int:
+        def helper_calculate(index):
+            result = 0
+            num = 0
+            sign = 1
+            while index < len(s):
+                if s[index].isdigit():
+                    num = num * 10 + int(s[index])
+                if s[index] == "+":
+                    result += num * sign
+                    num = 0
+                    sign = 1
+                if s[index] == "-":
+                    result += num * sign
+                    num = 0
+                    sign = -1
+                if s[index] == ")":
+                    result += num * sign
+                    return index, result
+                if s[index] == "(":
+                    index, result_in_brackers = helper_calculate(index + 1)
+                    result += result_in_brackers * sign
+                index += 1
+            result += num * sign
+            return result
+
+        return helper_calculate(0)
diff --git a/grind75_hard/06_224_Basic Calculator/level_3.py b/grind75_hard/06_224_Basic Calculator/level_3.py
new file mode 100644
index 0000000..d93808b
--- /dev/null
+++ b/grind75_hard/06_224_Basic Calculator/level_3.py	
@@ -0,0 +1,28 @@
+class Solution:
+    def calculate(self, s: str) -> int:
+        def helper_calculate(index):
+            num = 0
+            sign = 1
+            result = 0
+            while index < len(s):
+                if s[index].isdigit():
+                    num = 10 * num + int(s[index])
+                if s[index] == "+":
+                    result += num * sign
+                    num = 0
+                    sign = 1
+                if s[index] == "-":
+                    result += num * sign
+                    num = 0
+                    sign = -1
+                if s[index] == ")":
+                    result += num * sign
+                    return result, index
+                if s[index] == "(":
+                    result_in_brackets, index = helper_calculate(index + 1)
+                    result += result_in_brackets * sign
+                index += 1
+            result += num * sign
+            return result
+
+        return helper_calculate(0)
diff --git a/grind75_hard/06_224_Basic Calculator/level_4.py b/grind75_hard/06_224_Basic Calculator/level_4.py
new file mode 100644
index 0000000..96df556
--- /dev/null
+++ b/grind75_hard/06_224_Basic Calculator/level_4.py	
@@ -0,0 +1,38 @@
+# 再帰下降構文解析
+class Solution:
+    def calculate(self, s: str) -> int:
+        index = 0
+
+        def get_next_expression():
+            nonlocal index
+            index += 1
+            while index < len(s) and s[index].isspace():
+                index += 1
+
+        def expr():
+            nonlocal index
+            result = factor()
+            while index < len(s) and s[index] in "+-":
+                op = s[index]
+                get_next_expression()
+                if op == "+":
+                    result += factor()
+                else:
+                    result -= factor()
+            return result
+
+        def factor():
+            nonlocal index
+            result = 0
+            while index < len(s) and s[index].isdigit():
+                result = 10 * result + int(s[index])
+                get_next_expression()
+            if index < len(s) and s[index] == "(":
+                get_next_expression()
+                result = expr()
+                get_next_expression()  # ")"を読み飛ばす
+            return result
+
+        if index < len(s) and s[0].isspace():
+            get_next_expression()
+        return expr()
diff --git a/grind75_hard/06_224_Basic Calculator/level_5.py b/grind75_hard/06_224_Basic Calculator/level_5.py
new file mode 100644
index 0000000..543afb3
--- /dev/null
+++ b/grind75_hard/06_224_Basic Calculator/level_5.py	
@@ -0,0 +1,39 @@
+# 再帰下降構文解析
+class Solution:
+    def calculate(self, s: str) -> int:
+        index = 0
+
+        def skip_spaces():
+            nonlocal index
+            index += 1
+            while index < len(s) and s[index].isspace():
+                index += 1
+
+        def expr():
+            nonlocal index
+            result = factor()
+            while index < len(s) and s[index] in "+-":
+                op = s[index]
+                skip_spaces()
+                if op == "+":
+                    result += factor()
+                else:
+                    result -= factor()
+            return result
+
+        def factor():
+            nonlocal index
+            result = 0
+            if index < len(s) and s[index] == "(":
+                skip_spaces()
+                result = expr()
+                skip_spaces()  # ")"を読み飛ばす
+                return result
+            while index < len(s) and s[index].isdigit():
+                result = 10 * result + int(s[index])
+                skip_spaces()
+            return result
+
+        if index < len(s) and s[0].isspace():
+            skip_spaces()
+        return expr()
diff --git a/grind75_hard/06_224_Basic Calculator/level_6.py b/grind75_hard/06_224_Basic Calculator/level_6.py
new file mode 100644
index 0000000..495075d
--- /dev/null
+++ b/grind75_hard/06_224_Basic Calculator/level_6.py	
@@ -0,0 +1,40 @@
+# 再帰下降構文解析
+# スペースを最初に除去
+# result = 0のタイミングを修正
+# 単行演算子を明示的に処理
+class Solution:
+    def calculate(self, s: str) -> int:
+        index = 0
+
+        def expr():
+            nonlocal index
+            if index < len(s) and s[index] == "-":
+                index += 1
+                result = -factor()
+            else:
+                result = factor()
+
+            while index < len(s) and s[index] in "+-":
+                op = s[index]
+                index += 1
+                if op == "+":
+                    result += factor()
+                else:
+                    result -= factor()
+            return result
+
+        def factor():
+            nonlocal index
+            if index < len(s) and s[index] == "(":
+                index += 1
+                result = expr()
+                index += 1  # ")"を読み飛ばす
+                return result
+            result = 0
+            while index < len(s) and s[index].isdigit():
+                result = 10 * result + int(s[index])
+                index += 1
+            return result
+
+        s = s.replace(" ", "")
+        return expr()