## Ceiling in right side for every element in an array

Given an array of integers, find the closest greater element for every element. If there is no greater element then print -1

Examples:

Input : arr[] = {10, 5, 11, 10, 20, 12}
Output : 10 10 12 12 -1 -1

Input : arr[] = {50, 20, 200, 100, 30}
Output : 100 30 -1 -1 -1

A simple solution is to run two nested loops. We pick an outer element one by one. For every picked element, we traverse right side array and find closest greater or equal element. Time complexity of this solution is O(n*n)

A better solution is to use sorting. We sort all elements, then for every element, traverse toward right until we find a greater element (Note that there can be multiple occurrences of an element).

An efficient solution is to use Self Balancing BST (Implemented as set in C++ and TreeSet in Java). In a Self Balancing BST, we can do both insert and ceiling operations in O(Log n) time.

 import java.util.*;    class TreeSetDemo {     public static void closestGreater(int[] arr)     {         int n = arr.length;         TreeSet ts = new TreeSet();         ArrayList ceilings = new ArrayList(n);                              for (int i = n - 1; i >= 0; i--) {             Integer greater = ts.ceiling(arr[i]);             if (greater == null)                 ceilings.add(-1);             else                 ceilings.add(greater);             ts.add(arr[i]);         }            for (int i=n-1; i>=0; i--)            System.out.print(ceilings.get(i) + " ");     }        public static void main(String[] args)     {         int[] arr = {50, 20, 200, 100, 30};         closestGreater(arr);     } }

Time Complexity : O(n Log n)

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the “Improve Article” button below.

Article Tags :

Be the First to upvote.

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.