feat: add Coin Change

Author: wislertt

.templates/leetcode/json/coin_change.json

@@ -0,0 +1,46 @@
+{
+    "problem_name": "coin_change",
+    "solution_class_name": "Solution",
+    "problem_number": "322",
+    "problem_title": "Coin Change",
+    "difficulty": "Medium",
+    "topics": "Array, Dynamic Programming, Breadth-First Search",
+    "tags": [],
+    "readme_description": "You are given an integer array `coins` representing coins of different denominations and an integer `amount` representing a total amount of money.\n\nReturn the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins, return `-1`.\n\nYou may assume that you have an infinite number of each kind of coin.",
+    "readme_examples": [
+        {
+            "content": "```\nInput: coins = [1,2,5], amount = 11\nOutput: 3\n```\n**Explanation:** 11 = 5 + 5 + 1"
+        },
+        { "content": "```\nInput: coins = [2], amount = 3\nOutput: -1\n```" },
+        { "content": "```\nInput: coins = [1], amount = 0\nOutput: 0\n```" }
+    ],
+    "readme_constraints": "- `1 <= coins.length <= 12`\n- `1 <= coins[i] <= 2^31 - 1`\n- `0 <= amount <= 10^4`",
+    "readme_additional": "",
+    "solution_imports": "",
+    "solution_methods": [
+        {
+            "name": "coin_change",
+            "parameters": "coins: list[int], amount: int",
+            "return_type": "int",
+            "dummy_return": "-1"
+        }
+    ],
+    "test_imports": "import pytest\nfrom leetcode_py.test_utils import logged_test\nfrom .solution import Solution",
+    "test_class_name": "CoinChange",
+    "test_helper_methods": [
+        { "name": "setup_method", "parameters": "", "body": "self.solution = Solution()" }
+    ],
+    "test_methods": [
+        {
+            "name": "test_coin_change",
+            "parametrize": "coins, amount, expected",
+            "parametrize_typed": "coins: list[int], amount: int, expected: int",
+            "test_cases": "[([1, 2, 5], 11, 3), ([2], 3, -1), ([1], 0, 0), ([1, 3, 4], 6, 2), ([2, 5, 10, 1], 27, 4), ([5], 3, -1), ([1], 1, 1), ([1, 2], 2, 1), ([186, 419, 83, 408], 6249, 20)]",
+            "body": "result = self.solution.coin_change(coins, amount)\nassert result == expected"
+        }
+    ],
+    "playground_imports": "from solution import Solution",
+    "playground_test_case": "# Example test case\ncoins = [1, 2, 5]\namount = 11\nexpected = 3",
+    "playground_execution": "result = Solution().coin_change(coins, amount)\nresult",
+    "playground_assertion": "assert result == expected"
+}

Makefile

@@ -1,5 +1,5 @@
 PYTHON_VERSION = 3.13
-PROBLEM ?= reverse_linked_list
+PROBLEM ?= coin_change
 FORCE ?= 0
 COMMA := ,
 

leetcode/coin_change/README.md

@@ -0,0 +1,46 @@
+# Coin Change
+
+**Difficulty:** Medium
+**Topics:** Array, Dynamic Programming, Breadth-First Search
+**Tags:**
+
+**LeetCode:** [Problem 322](https://leetcode.com/problems/coin-change/description/)
+
+## Problem Description
+
+You are given an integer array `coins` representing coins of different denominations and an integer `amount` representing a total amount of money.
+
+Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins, return `-1`.
+
+You may assume that you have an infinite number of each kind of coin.
+
+## Examples
+
+### Example 1:
+
+```
+Input: coins = [1,2,5], amount = 11
+Output: 3
+```
+
+**Explanation:** 11 = 5 + 5 + 1
+
+### Example 2:
+
+```
+Input: coins = [2], amount = 3
+Output: -1
+```
+
+### Example 3:
+
+```
+Input: coins = [1], amount = 0
+Output: 0
+```
+
+## Constraints
+
+- `1 <= coins.length <= 12`
+- `1 <= coins[i] <= 2^31 - 1`
+- `0 <= amount <= 10^4`

leetcode/coin_change/__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",
+    "coins = [1, 2, 5]\n",
+    "amount = 11\n",
+    "expected = 3"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "execute",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "3"
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "result = Solution().coin_change(coins, amount)\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/coin_change/playground.ipynb

@@ -0,0 +1,21 @@
+class Solution:
+    # Time: O(amount * len(coins))
+    # Space: O(amount)
+    def coin_change(self, coins: list[int], amount: int) -> int:
+        if amount == 0:
+            return 0
+
+        # Initialize dp array with amount + 1 (impossible value)
+        # Since max coins needed is amount (using all 1-cent coins)
+        # amount + 1 serves as "infinity" to indicate impossible cases
+        dp = [amount + 1] * (amount + 1)
+
+        dp[0] = 0
+
+        for i in range(1, amount + 1):
+            for coin in coins:
+                if coin <= i:
+                    dp[i] = min(dp[i], dp[i - coin] + 1)
+
+        # Return result: -1 if impossible, otherwise minimum coins needed
+        return dp[amount] if dp[amount] <= amount else -1

leetcode/coin_change/solution.py

@@ -0,0 +1,31 @@
+import pytest
+
+from leetcode_py.test_utils import logged_test
+
+from .solution import Solution
+
+
+class TestCoinChange:
+    def setup_method(self):
+        self.solution = Solution()
+
+    @pytest.mark.parametrize(
+        "coins, amount, expected",
+        [
+            ([1, 2, 5], 11, 3),
+            ([2], 3, -1),
+            ([1], 0, 0),
+            ([1, 3, 4], 6, 2),
+            ([2, 5, 10, 1], 27, 4),
+            ([10, 1, 2, 5], 27, 4),
+            ([5], 3, -1),
+            ([5, 2], 3, -1),
+            ([1], 1, 1),
+            ([1, 2], 2, 1),
+            ([186, 419, 83, 408], 6249, 20),
+        ],
+    )
+    @logged_test
+    def test_coin_change(self, coins: list[int], amount: int, expected: int):
+        result = self.solution.coin_change(coins, amount)
+        assert result == expected

leetcode/coin_change/tests.py

@@ -22,8 +22,8 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Original: [1, 2, 3, 4, 5]\n",
-      "Expected: [5, 4, 3, 2, 1]\n"
+      "Original: 1 -> 2 -> 3 -> 4 -> 5\n",
+      "Expected: 5 -> 4 -> 3 -> 2 -> 1\n"
      ]
     }
    ],
@@ -41,21 +41,89 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 3,
    "id": "execute",
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Result: [5, 4, 3, 2, 1]\n"
+      "Result: 5 -> 4 -> 3 -> 2 -> 1\n"
      ]
     },
     {
      "data": {
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      "execution_count": 3,
@@ -75,15 +143,7 @@
    "execution_count": 4,
    "id": "test",
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "✅ Test passed! Linked list successfully reversed.\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "# Verify the result matches expected output\n",
     "assert result == expected"