Add JS spiral matrix LC medium solution

Author: nwthomas

src/leetcode/medium/spiral-matrix/spiralMatrix.js

@@ -0,0 +1,76 @@
+/*
+https://leetcode.com/problems/spiral-matrix/
+
+Given an m x n matrix, return all elements of the matrix in spiral order.
+
+Example 1:
+Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
+Output: [1,2,3,6,9,8,7,4,5]
+
+Example 2:
+Input: matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
+Output: [1,2,3,4,8,12,11,10,9,5,6,7]
+
+Constraints:
+m == matrix.length
+n == matrix[i].length
+1 <= m, n <= 10
+-100 <= matrix[i][j] <= 100
+*/
+
+const RIGHT = "right";
+const DOWN = "down";
+const LEFT = "left";
+const UP = "up";
+
+const spiralOrder = (matrix) => {
+    const result = [];
+    // Can be: "right", "down", "left", "up"
+    let direction = RIGHT;
+    let offset = 0;
+    let x = 0;
+    let y = 0;
+
+    while (true) {
+        result.push(matrix[y][x]);
+
+        if (direction == RIGHT) {
+            if (x < matrix[0].length - 1 - offset) {
+                x += 1;
+            } else {
+                direction = DOWN;
+                y += 1;
+            }
+        } else if (direction === DOWN) {
+            if (y < matrix.length - 1 - offset) {
+                y += 1;
+            } else {
+                direction = LEFT;
+                x -= 1;
+            }
+        } else if (direction === LEFT) {
+            if (x > 0 + offset) {
+                x -= 1;
+            } else {
+                direction = UP;
+                offset += 1;
+                y -= 1;
+            }
+        } else {
+            if (y > 0 + offset) {
+                y -= 1;
+            } else {
+                direction = RIGHT;
+                x += 1;
+            }
+        }
+
+        if (result.length === matrix.length * matrix[0].length) {
+            break;
+        }
+    }
+
+    return result;
+};
+
+module.exports = { spiralOrder };

src/leetcode/medium/spiral-matrix/spiralMatrix.test.js

@@ -0,0 +1,17 @@
+const { spiralOrder } = require("./spiralMatrix");
+
+describe("spiralOrder", () => {
+    it("returns the correct spiral order for a list with one array of one integer", () => {
+        const result = spiralOrder([[0]]);
+        expect(result).toEqual([0]);
+    });
+
+    it("returns the correct spiral order for a 2D matrix", () => {
+        const result = spiralOrder([
+            [1, 2, 3],
+            [4, 5, 6],
+            [7, 8, 9],
+        ]);
+        expect(result).toEqual([1, 2, 3, 6, 9, 8, 7, 4, 5]);
+    });
+});