add sprial matrix

Author: Connor Leech

udemy-interview-bootcamp-course/spiral_matrix.js

@@ -0,0 +1,63 @@
+// --- Directions
+// Write a function that accepts an integer N
+// and returns a NxN spiral matrix.
+// --- Examples
+//   matrix(2)
+//     [[undefined, undefined],
+//     [undefined, undefined]]
+//   matrix(3)
+//     [[1, 2, 3],
+//     [8, 9, 4],
+//     [7, 6, 5]]
+//  matrix(4)
+//     [[1,   2,  3, 4],
+//     [12, 13, 14, 5],
+//     [11, 16, 15, 6],
+//     [10,  9,  8, 7]]
+
+function matrix(n) {
+  const results = [];
+
+  for (let i = 0; i < n; i++) {
+    results.push([]);
+  }
+
+  let counter = 1;
+  let startColumn = 0;
+  let endColumn = n - 1;
+  let startRow = 0;
+  let endRow = n - 1;
+  while (startColumn <= endColumn && startRow <= endRow) {
+    // Top row
+    for (let i = startColumn; i <= endColumn; i++) {
+      results[startRow][i] = counter;
+      counter++;
+    }
+    startRow++;
+
+    // Right column
+    for (let i = startRow; i <= endRow; i++) {
+      results[i][endColumn] = counter;
+      counter++;
+    }
+    endColumn--;
+
+    // Bottom row
+    for (let i = endColumn; i >= startColumn; i--) {
+      results[endRow][i] = counter;
+      counter++;
+    }
+    endRow--;
+
+    // start column
+    for (let i = endRow; i >= startRow; i--) {
+      results[i][startColumn] = counter;
+      counter++;
+    }
+    startColumn++;
+  }
+
+  return results;
+}
+
+module.exports = matrix;