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Find closest greater value for every element in array

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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, 6, 20, 12} 
Output : 11 6 12 10 -1 20

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

A simple solution is to run two nested loops. We pick an outer element one by one. For every picked element, we traverse remaining array and find closest greater element. The 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 closest greater operations in O(Log n) time

Implementation:

C++




// C++ program to find closest greater value
// for every array element
#include <bits/stdc++.h>
using namespace std;
 
void closetGreater(int arr[], int n)
{
    // Insert all array elements into a Set
    set<int> ts;
    for (int i = 0; i < n; i++)
        ts.insert(arr[i]);
 
    // Find smallest greater element for
    // every array element
    for (int i = 0; i < n; i++)
    {
        auto greater = ts.upper_bound(arr[i]);
 
        if (greater == ts.end())
            cout << -1 << " ";
        else
            cout << *greater << " ";
    }
}
 
// Driver code
int main(int argc, char const *argv[])
{
    int arr[] = {10, 5, 11, 10, 20, 12};
    int n = sizeof(arr) / sizeof(arr[0]);
    closetGreater(arr, n);
    return 0;
}
 
// This code is contributed by
// sanjeev2552


Java




// Java program to find closest greater value for
// every array element
import java.util.*;
 
class TreeSetDemo {
    public static void closestGreater(int[] arr)
    {
        // Insert all array elements into a TreeSet
        TreeSet<Integer> ts = new TreeSet<Integer>();
        for (int i = 0; i < arr.length; i++)
            ts.add(arr[i]);
 
        // Find smallest greater element for every
        // array element
        for (int i = 0; i < arr.length; i++) {
            Integer greater = ts.higher(arr[i]);
            if (greater == null)
                System.out.print(-1 + " ");
            else
                System.out.print(greater + " ");
        }
    }
 
    public static void main(String[] args)
    {
        int[] arr = { 10, 5, 11, 10, 20, 12};
        closestGreater(arr);
    }
}


Python3




# Python program to find closest greater value
# for every array element
def upper_bound(s, val):
    temp = list(s).copy()
    temp.sort()
    try:
        index_value = temp.index(val)
        if(index_value == len(temp)-1):
            return 0
        return temp[index_value+1]
    except ValueError:
        return arr[0]
 
def closetGreater(arr, n):
    # Insert all array elements into a Set
    ts = set()
    for i in range(n):
        ts.add(arr[i])
 
    # Find smallest greater element for
    # every array element
    for i in range(n):
        greater = upper_bound(ts, arr[i])
 
        if (greater == 0):
            print(-1,end = " ")
        else:
            print(greater,end = " ")
     
# Driver code
arr = [10, 5, 11, 10, 20, 12]
n = len(arr)
closetGreater(arr, n)
 
 
# This code is contributed by shinjanpatra


C#




// C# program to find closest greater value for
// every array element
using System;
using System.Collections.Generic;
 
public class TreeSetDemo {
  public static void closestGreater(int[] arr)
  {
     
    // Insert all array elements into a TreeSet
    SortedSet<int> ts = new SortedSet<int>();
    for (int i = 0; i < arr.Length; i++)
      ts.Add(arr[i]);
 
    // Find smallest greater element for every
    // array element
    for (int i = 0; i < arr.Length; i++) {
      int greater = upper_bound(ts, arr[i]);
      if (greater == -1)
        Console.Write(-1 + " ");
      else
        Console.Write(greater + " ");
    }
  }
  public static int upper_bound(SortedSet<int> s, int val)
  {
    List<int> temp = new List<int>();
    temp.AddRange(s);
    temp.Sort();
    if (temp.IndexOf(val) + 1 == temp.Count)
      return -1;
    else
      return temp[temp.IndexOf(val) + 1];
  }
  public static void Main(String[] args)
  {
    int[] arr = { 10, 5, 11, 10, 20, 12 };
    closestGreater(arr);
  }
}
 
// This code is contributed by Rajput-Ji


Javascript




<script>
 
// JavaScript program to find closest greater value
// for every array element
 
function closetGreater(arr, n) {
    // Insert all array elements into a Set
    let ts = new Set();
    for (let i = 0; i < n; i++)
        ts.add(arr[i]);
 
    // Find smallest greater element for
    // every array element
    for (let i = 0; i < n; i++) {
        let greater = upper_bound(ts, arr[i]);
 
        if (!greater)
            document.write(-1 + " ");
        else
            document.write(greater + " ");
    }
}
 
function upper_bound(s, val) {
    let temp = [...s];
    temp.sort((a, b) => a - b);
    return temp[temp.indexOf(val) + 1];
}
 
// Driver code
 
let arr = [10, 5, 11, 10, 20, 12];
let n = arr.length;
closetGreater(arr, n);
 
 
// This code is contributed by _saurabh_jaiswal
 
</script>


Output

11 10 12 11 -1 20 

Time Complexity: O(n Log n)



Last Updated : 09 Sep, 2022
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