Merge pull request neetcode-gh#2066 from andrewmustea/add_0589-n-ary-…

…tree-preorder-traversal.c

create 0589-n-ary-tree-preorder-traversal.c

c/0589-n-ary-tree-preorder-traversal.c

@@ -0,0 +1,42 @@
+/**
+ * Given the root of an n-ary tree, return the preorder traversal of its nodes'
+ * values.
+ *
+ * Nary-Tree input serialization is represented in their level order traversal.
+ * Each group of children is separated by the null value (See examples)
+ *
+ * Constraints:
+ *
+ * The number of nodes in the tree is in the range [0, 104].
+ * 0 <= Node.val <= 10^4
+ * The height of the n-ary tree is less than or equal to 1000.
+ *
+ * Definition for a Node.
+ * struct Node {
+ *     int val;
+ *     int numChildren;
+ *     struct Node** children;
+ * };
+ *
+ * Note: The returned array must be malloced, assume caller calls free().
+ *
+ * Space: O(n)
+ * Time: O(n)
+ */
+
+void traverse(struct Node* root, int *ret, int* index) {
+    if (!root)
+        return;
+
+    ret[(*index)++] = root->val;
+
+    for (int i = 0; i < root->numChildren; ++i)
+        traverse(root->children[i], ret, index);
+}
+
+int* preorder(struct Node* root, int* returnSize) {
+    int *ret = malloc(10000 * sizeof(int));
+    *returnSize = 0;
+    traverse(root, ret, returnSize);
+    return ret;
+}