INORDER AND PREORDER ARE GIVEN.
SO FOR THE PURPOSE OF FINDING THE ROOT NODE THAT CAN BE DONE IN O(1) TIME(COZ PREORDER GIVEN).
NOW OUR TASK IS FINDING THE LEFT SUBTREE AND RIGHT SUBTREEE...SO FOR THAT PURPOSE THE ELEMENT WHICH WE TAKEN AS ROOT...WE HAVE TO SEARCH THAT ELEMENT IN THE GIVEN INODER OF TREE..AND THIS LINEAR SEARCH TAKES O(N) TIME FOR ONE ELEMENT
REPEAT THIS PROCEDURE FOR ALL ELEMENTS...MEANS N times linear search is requird...so time complexity will be O(N^2)