Serialize and Deserialize n-ary tree

Given an N-ary Tree, Serialize and Deserialize it. Serialization is a basically a representation of a tree in a String format which takes much lesser space than storing the tree itself. Deserialization is constructing the actual tree using the serialized format of the tree.

Spiral Matrix

Given an m x n matrix, return all elements of the matrix in spiral order. The Spiral Matrix problem takes a 2-Dimensional array of N-rows and M-columns as an input, and prints the elements of this matrix in spiral order.

Next Greater Element I

You are given two integer arrays nums1 and nums2 both of unique elements, where nums1 is a subset of nums2. Find all the next greater numbers for nums1’s elements in the corresponding places of nums2. The Next Greater Number of a number x in nums1 is the first greater number to its right in nums2. If it does not exist, return -1 for this number.