Add Binary

0067.Add-Binary/memo.md

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+# 67. Add Binary
+
+## step1
+組み込み関数を使えば簡単。
+
+## step2
+
+`itertools.zip_longest` を使う。二進法の加算を愚直に実装。
+
+https://github.com/NobukiFukui/Grind75-ProgrammingTraining/pull/35
+
+
+https://github.com/huyfififi/coding-challenges/pull/20
+
+> deque() を使うと reverse 処理が省けて、かつ、手計算のときと同じように考えられるのでいいですね
+
+
+https://github.com/ryosuketc/leetcode_grind75/pull/20
+
+
+zfillは知らなかった。
+https://docs.python.org/ja/3/library/stdtypes.html#str.zfill

0067.Add-Binary/step1.py

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+class Solution:
+    def addBinary(self, a: str, b: str) -> str:
+        return bin(int(a, 2) + int(b, 2))[2:]

0067.Add-Binary/step2.py

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+import itertools
+
+
+class Solution:
+    def addBinary(self, a: str, b: str) -> str:
+        reversed_result = []
+        carry = False
+        for c_a, c_b in itertools.zip_longest(a[::-1], b[::-1], fillvalue="0"):
+            if c_a == "0" and c_b == "0" and carry:
+                reversed_result.append("1")
+                carry = False
+            elif c_a == "0" and c_b == "0" and not carry:
+                reversed_result.append("0")
+                carry = False
+            elif c_a == "1" and c_b == "1" and carry:
+                reversed_result.append("1")
+                carry = True
+            elif c_a == "1" and c_b == "1" and not carry:
+                reversed_result.append("0")
+                carry = True
+            elif carry:
+                reversed_result.append("0")
+                carry = True
+            else:
+                reversed_result.append("1")
+                carry = False
+        if carry:
+            reversed_result.append("1")
+        return "".join(reversed(reversed_result))
+
+
+class Solution:
+    def addBinary(self, a: str, b: str) -> str:
+        i = len(a) - 1
+        j = len(b) - 1
+        carry = 0
+        reversed_result = []
+        while i >= 0 or j >= 0 or carry == 1:
+            total = carry
+            if i >= 0:
+                total += int(a[i])
+            if j >= 0:
+                total += int(b[j])
+            reversed_result.append(str(total % 2))
+            carry = total // 2
+            i -= 1
+            j -= 1
+        return "".join(reversed(reversed_result))
+
+
+from collections import deque
+
+
+class Solution:
+    def addBinary(self, a: str, b: str) -> str:
+        n = max(len(a), len(b))
+        padded_a = a.zfill(n)
+        padded_b = b.zfill(n)
+        result = deque()
+        carry = 0
+        for i in range(n - 1, -1, -1):
+            total = int(padded_a[i]) + int(padded_b[i]) + carry
+            result.appendleft(str(total % 2))
+            carry = total // 2
+        if carry == 1:
+            result.appendleft("1")
+        return "".join(result)