feat: add preOrder algorithm for tree data structure. test: add testc…

Data-Structures/Tree/PreOrder.js

@@ -0,0 +1,10 @@
+function preOrder (root) {
+  if (root === null) return []
+
+  const left = preOrder(root.left)
+  const right = preOrder(root.right)
+
+  return [root.value, ...left, ...right]
+}
+
+export { preOrder }

Data-Structures/Tree/test/PreOrder.test.js

@@ -0,0 +1,92 @@
+import { preOrder } from '../PreOrder'
+
+describe('preOrder function', () => {
+  test('should return an empty array for an empty tree', () => {
+    const tree = null
+    expect(preOrder(tree)).toEqual([])
+  })
+
+  test('should return an array with the root value for a tree with only one node', () => {
+    const tree = {
+      value: 5,
+      left: null,
+      right: null
+    }
+    expect(preOrder(tree)).toEqual([5])
+  })
+
+  test('should return the correct array for a tree with multiple nodes', () => {
+    const tree = {
+      value: 5,
+      left: {
+        value: 3,
+        left: {
+          value: 2,
+          left: null,
+          right: null
+        },
+        right: {
+          value: 4,
+          left: null,
+          right: null
+        }
+      },
+      right: {
+        value: 7,
+        left: {
+          value: 6,
+          left: null,
+          right: null
+        },
+        right: {
+          value: 8,
+          left: null,
+          right: null
+        }
+      }
+    }
+    expect(preOrder(tree)).toEqual([5, 3, 2, 4, 7, 6, 8])
+  })
+
+  test('should return the correct array for a tree with a single branch to the left', () => {
+    const tree = {
+      value: 5,
+      left: {
+        value: 4,
+        left: {
+          value: 3,
+          left: {
+            value: 2,
+            left: null,
+            right: null
+          },
+          right: null
+        },
+        right: null
+      },
+      right: null
+    }
+    expect(preOrder(tree)).toEqual([5, 4, 3, 2])
+  })
+
+  test('should return the correct array for a tree with a single branch to the right', () => {
+    const tree = {
+      value: 5,
+      left: null,
+      right: {
+        value: 6,
+        left: null,
+        right: {
+          value: 7,
+          left: null,
+          right: {
+            value: 8,
+            left: null,
+            right: null
+          }
+        }
+      }
+    }
+    expect(preOrder(tree)).toEqual([5, 6, 7, 8])
+  })
+})