add: leetcode 0559 solution

leetcode/0559.Maximum-Depth-of-N-ary-Tree/559.Maximum Depth of N-ary Tree.go

@@ -0,0 +1,32 @@
+package leetcode
+
+type Node struct {
+	Val      int
+	Children []*Node
+}
+
+func maxDepth(root *Node) int {
+	if root == nil {
+		return 0
+	}
+	return 1 + bfs(root)
+}
+
+func bfs(root *Node) int {
+	var q []*Node
+	var depth int
+	q = append(q, root.Children...)
+	for len(q) != 0 {
+		depth++
+		length := len(q)
+		for length != 0 {
+			ele := q[0]
+			q = q[1:]
+			length--
+			if ele != nil && len(ele.Children) != 0 {
+				q = append(q, ele.Children...)
+			}
+		}
+	}
+	return depth
+}