feat: add Add Binary problem

Author: wislertt

.templates/leetcode/json/add_binary.json

@@ -0,0 +1,43 @@
+{
+    "problem_name": "add_binary",
+    "solution_class_name": "Solution",
+    "problem_number": "67",
+    "problem_title": "Add Binary",
+    "difficulty": "Easy",
+    "topics": "Math, String, Bit Manipulation, Simulation",
+    "tags": ["grind-75"],
+    "readme_description": "Given two binary strings `a` and `b`, return *their sum as a binary string*.",
+    "readme_examples": [
+        { "content": "```\nInput: a = \"11\", b = \"1\"\nOutput: \"100\"\n```" },
+        { "content": "```\nInput: a = \"1010\", b = \"1011\"\nOutput: \"10101\"\n```" }
+    ],
+    "readme_constraints": "- `1 <= a.length, b.length <= 10^4`\n- `a` and `b` consist only of `'0'` or `'1'` characters.\n- Each string does not contain leading zeros except for the zero itself.",
+    "readme_additional": "",
+    "solution_imports": "",
+    "solution_methods": [
+        {
+            "name": "add_binary",
+            "parameters": "a: str, b: str",
+            "return_type": "str",
+            "dummy_return": "\"\""
+        }
+    ],
+    "test_imports": "import pytest\nfrom leetcode_py.test_utils import logged_test\nfrom .solution import Solution",
+    "test_class_name": "AddBinary",
+    "test_helper_methods": [
+        { "name": "setup_method", "parameters": "", "body": "self.solution = Solution()" }
+    ],
+    "test_methods": [
+        {
+            "name": "test_add_binary",
+            "parametrize": "a, b, expected",
+            "parametrize_typed": "a: str, b: str, expected: str",
+            "test_cases": "[('11', '1', '100'), ('1010', '1011', '10101'), ('0', '0', '0'), ('1', '1', '10'), ('1111', '1111', '11110')]",
+            "body": "result = self.solution.add_binary(a, b)\nassert result == expected"
+        }
+    ],
+    "playground_imports": "from solution import Solution",
+    "playground_test_case": "# Example test case\na = '11'\nb = '1'\nexpected = '100'",
+    "playground_execution": "result = Solution().add_binary(a, b)\nresult",
+    "playground_assertion": "assert result == expected"
+}

Makefile

@@ -1,5 +1,5 @@
 PYTHON_VERSION = 3.13
-PROBLEM ?= maximum_depth_of_binary_tree
+PROBLEM ?= add_binary
 FORCE ?= 0
 COMMA := ,
 

leetcode/add_binary/README.md

@@ -0,0 +1,33 @@
+# Add Binary
+
+**Difficulty:** Easy
+**Topics:** Math, String, Bit Manipulation, Simulation
+**Tags:** grind-75
+
+**LeetCode:** [Problem 67](https://leetcode.com/problems/add-binary/description/)
+
+## Problem Description
+
+Given two binary strings `a` and `b`, return _their sum as a binary string_.
+
+## Examples
+
+### Example 1:
+
+```
+Input: a = "11", b = "1"
+Output: "100"
+```
+
+### Example 2:
+
+```
+Input: a = "1010", b = "1011"
+Output: "10101"
+```
+
+## Constraints
+
+- `1 <= a.length, b.length <= 10^4`
+- `a` and `b` consist only of `'0'` or `'1'` characters.
+- Each string does not contain leading zeros except for the zero itself.

leetcode/add_binary/__init__.py

@@ -0,0 +1,80 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "imports",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from solution import Solution"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "id": "setup",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Example test case\n",
+    "a = \"11\"\n",
+    "b = \"1\"\n",
+    "expected = \"100\""
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "execute",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'100'"
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "result = Solution().add_binary(a, b)\n",
+    "result"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "test",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "assert result == expected"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "leetcode-py-py3.13",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.13.7"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

leetcode/add_binary/playground.ipynb

@@ -0,0 +1,26 @@
+class Solution:
+    # Time: O(len(a) + len(b))
+    # Space: O(len(a) + len(b))
+    def add_binary(self, a: str, b: str) -> str:
+        # int(a, 2) converts binary string to decimal: int("11", 2) → 3
+        # bin() converts decimal to binary string with prefix: bin(3) → '0b11'
+        # [2:] removes the '0b' prefix to get just binary digits
+        return bin(int(a, 2) + int(b, 2))[2:]
+
+
+# Python Base Conversion:
+#
+# String → Integer (using int() with base parameter):
+# - int("1010", 2) → 10 (binary to decimal)
+# - int("ff", 16) → 255 (hex to decimal)
+# - int("10", 8) → 8 (octal to decimal)
+#
+# Integer → String (conversion functions add prefixes):
+# - bin(10) → '0b1010' (binary with '0b' prefix)
+# - hex(255) → '0xff' (hex with '0x' prefix)
+# - oct(8) → '0o10' (octal with '0o' prefix)
+#
+# These prefixes match Python literal syntax:
+# - 0b1010 = 10, 0xff = 255, 0o10 = 8
+#
+# For string problems, slice off the prefix: bin(n)[2:] gives just the digits.

leetcode/add_binary/solution.py

@@ -0,0 +1,25 @@
+import pytest
+
+from leetcode_py.test_utils import logged_test
+
+from .solution import Solution
+
+
+class TestAddBinary:
+    def setup_method(self):
+        self.solution = Solution()
+
+    @pytest.mark.parametrize(
+        "a, b, expected",
+        [
+            ("11", "1", "100"),
+            ("1010", "1011", "10101"),
+            ("0", "0", "0"),
+            ("1", "1", "10"),
+            ("1111", "1111", "11110"),
+        ],
+    )
+    @logged_test
+    def test_add_binary(self, a: str, b: str, expected: str):
+        result = self.solution.add_binary(a, b)
+        assert result == expected