Its a wrap

Author: vfarah-if

test-pnpm/song_birds/README.md

@@ -103,3 +103,9 @@ function factorial(n: number): number {
 }
 ```
 
+1. **Strategy Pattern**: Used a strategy object (`songCalculator`) to map the number of birds to their respective calculation functions.
+2. **Code Organisation**: Each calculation is encapsulated in its own function, making the code more readable.
+3. **Explicit Constants**: Added the `BRANCH_COUNT` constant to make the code more maintainable.
+4. **Removed Hardcoded Arrays**: Instead of hardcoding the arrays of combinations and permutations, the code now calculates the number of combinations and permutations directly.
+5. **Added Documentation**: Each calculation includes comments explaining the logic behind it.
+6. **Consistent Return**: The function always returns 0 for invalid bird counts (greater than 3 or less than 0).

test-pnpm/song_birds/song.birds.ts

@@ -1,42 +1,25 @@
 export function countUniqueSongs(birds: Array<string>): number {
   if (!birds || birds.length === 0) return 0;
-  if (birds.length === 1) {
-    const birdCombos = [['A']]; // 1 bird
-    const branchCombos = [['1'], ['2'], ['3']]; // each possible branch
-    return birdCombos.length * branchCombos.length; // 1 * 3 = 3
-  }
-  if (birds.length === 2) {
-    const birdCombos = [
-      ['A', 'B'],
-      ['A', 'C'],
-      ['B', 'C'],
-    ];
-    const branchCombos = [
-      ['1', '2'],
-      ['1', '3'],
-      ['2', '3'],
-    ];
-    return birdCombos.length * branchCombos.length * factorial(2);
-  }
-  if (birds.length === 3) {
-    const permutationsOfBirds = [
-      ['A', 'B', 'C'],
-      ['A', 'C', 'B'],
-      ['B', 'A', 'C'],
-      ['B', 'C', 'A'],
-      ['C', 'A', 'B'],
-      ['C', 'B', 'A'],
-    ];
-    const permutationsOfBranches = [
-      ['1', '2', '3'],
-      ['1', '3', '2'],
-      ['2', '1', '3'],
-      ['2', '3', '1'],
-      ['3', '1', '2'],
-      ['3', '2', '1'],
-    ];
-    return permutationsOfBirds.length * permutationsOfBranches.length;
-  }
+
+  const BRANCH_COUNT = 3;
+  const birdCount = birds.length;
+
+  const songCalculator = {
+    1: () => BRANCH_COUNT, // One bird can perch on any of the 3 branches
+    2: () => {
+      const birdCombinations = 3; // Number of ways to choose 2 birds from the set
+      const branchCombinations = 3; // Number of ways to choose 2 branches from 3
+      const birdPermutations = factorial(2); // Number of ways to arrange 2 birds
+      return birdCombinations * branchCombinations * birdPermutations; // 3 * 3 * 2 = 18
+    },
+    3: () => {
+      const birdPermutations = factorial(3); // Number of ways to arrange 3 birds
+      const branchPermutations = factorial(3); // Number of ways to arrange 3 branches
+      return birdPermutations * branchPermutations; // 6 * 6 = 36
+    },
+  };
+
+  return songCalculator[birdCount] ? songCalculator[birdCount]() : 0;
 }
 
 function factorial(n: number): number {