Smallest greater elements in whole array

An array is given of n length, and we need to calculate the next greater element for each element in given array. If next greater element is not available in given array then we need to fill ‘_’ at that index place.

Examples :

Input :  6 3 9 8 10 2 1 15 7 
Output : 7 6 10 9 15 3 2 _ 8
Here every element of array has next greater 
element but at index 7,
15 is the greatest element of given array
and no other element is greater from 15 
so at the index of 15 we fill with '_' .

Input  : 13 6 7 12
Output : _ 7 12 13
Here, at index 0, 13 is the greatest 
value in given array and no other 
array element is greater from 13 so
at index 0 we fill '_'.

Asked in : Zoho



A simple solution is to use two loops nested. The outer loop picks all elements one by one and inner loop finds the next greater element by linearly searching from beginning to end.

C++

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// Simple CPP program to find smallest
// greater element in whole array for 
// every element.
#include <bits/stdc++.h>
using namespace std;
  
void smallestGreater(int arr[], int n)
{
    for (int i = 0; i < n; i++) {
  
        // Find the closest greater element 
        // for arr[j] in the entire array.
        int diff = INT_MAX, closest = -1;
        for (int j = 0; j < n; j++) {
            if ( arr[i] < arr[j] && 
                 arr[j] - arr[i] < diff)
            {
                diff = arr[j] - arr[i];
                closest = j;            
            }
        }
          
        // Check if arr[i] is largest
        (closest == -1)?  cout << "_ " 
              cout << arr[closest] << " ";
     }
}
  
// Driver code
int main()
{
    int ar[] = { 6, 3, 9, 8, 10, 2, 1, 15, 7 };
    int n = sizeof(ar) / sizeof(ar[0]);
    smallestGreater(ar, n);
    return 0;
}

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Java

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// Simple Java program to find
// smallest greater element in 
// whole array for every element.
import java.io.*;
  
class GFG 
{
static void smallestGreater(int arr[], 
                            int n)
{
    for (int i = 0; i < n; i++) 
    {
  
        // Find the closest greater
        // element for arr[j] in 
        // the entire array.
        int diff = Integer.MAX_VALUE;
        int closest = -1;
        for (int j = 0; j < n; j++) 
        {
            if (arr[i] < arr[j] && 
                arr[j] - arr[i] < diff)
            {
                diff = arr[j] - arr[i];
                closest = j;         
            }
        }
          
        // Check if arr[i] is largest
        if(closest == -1)
        System.out.print( "_ " );
        else
        System.out.print(arr[closest] + " ");
    }
}
  
// Driver code
public static void main (String[] args) 
{
    int ar[] = {6, 3, 9, 8, 10
                2, 1, 15, 7};
    int n = ar.length;
    smallestGreater(ar, n);
}
}
  
// This code is contributed by anuj_67.

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Python3

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# Simple Python program to find smallest
# greater element in whole array for 
# every element.
def smallestGreater(arr, n) :
    for i in range(0, n) :
  
        # Find the closest greater element 
        # for arr[j] in the entire array.
        diff = 1000
        closest = -1;
        for j in range(0, n) :
            if ( arr[i] < arr[j] and 
                  arr[j] - arr[i] < diff) :
                diff = arr[j] - arr[i];
                closest = j;     
          
        # Check if arr[i] is largest
        if (closest == -1) :
            print ("_ ", end = "");
        else :
            print ("{} ".format(arr[closest]),
                                    end = "");
  
# Driver code
ar = [6, 3, 9, 8, 10, 2, 1, 15, 7];
n = len(ar) ;
smallestGreater(ar, n);
  
# This code is contributed by Manish Shaw
# (manishshaw1)

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C#

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// Simple C# program to find
// smallest greater element in 
// whole array for every element.
using System;
  
class GFG 
{
static void smallestGreater(int []arr, 
                            int n)
{
    for (int i = 0; i < n; i++) 
    {
  
        // Find the closest greater
        // element for arr[j] in 
        // the entire array.
        int diff = int.MaxValue;
        int closest = -1;
        for (int j = 0; j < n; j++) 
        {
            if (arr[i] < arr[j] && 
                arr[j] - arr[i] < diff)
            {
                diff = arr[j] - arr[i];
                closest = j;         
            }
        }
          
        // Check if arr[i] is largest
        if(closest == -1)
        Console.Write( "_ " );
        else
        Console.Write(arr[closest] + " ");
    }
}
  
// Driver code
public static void Main() 
{
    int []ar = {6, 3, 9, 8, 10, 
                2, 1, 15, 7};
    int n = ar.Length;
    smallestGreater(ar, n);
}
}
  
// This code is contributed by anuj_67.

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PHP

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<?php
// Simple PHP program to find smallest
// greater element in whole array for 
// every element.
  
function smallestGreater($arr, $n)
{
    for ( $i = 0; $i < $n; $i++) {
  
        // Find the closest greater element 
        // for arr[j] in the entire array.
        $diff = PHP_INT_MAX; $closest = -1;
        for ( $j = 0; $j < $n; $j++) {
            if ( $arr[$i] < $arr[$j] && 
                $arr[$j] - $arr[$i] < $diff)
            {
                $diff = $arr[$j] - $arr[$i];
                $closest = $j;     
            }
        }
          
        // Check if arr[i] is largest
        if ($closest == -1)
        echo "_ " ;
        else
            echo $arr[$closest] , " ";
    }
}
  
    // Driver code
    $ar = array (6, 3, 9, 8, 10, 2, 1, 15, 7);
    $n = sizeof($ar) ;
    smallestGreater($ar, $n);
  
// This code is contributed by ajit
?>

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Output:

7 6 10 9 15 3 2 _ 8

Time Complexity : O(n*n)
Auxiliary Space: O(1)

An efficient solution is to one by one insert elements in a set (A self balancing binary search tree). After inserting into set, we search elements. After we find iterator of the searched element, we move iterator to next (note that set stores elements in sorted order) to find element which is just greater.

C++

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// Efficient CPP program to find smallest
// greater element in whole array for 
// every element.
#include <bits/stdc++.h>
using namespace std;
  
void smallestGreater(int arr[], int n)
{
    set<int> s;
    for (int i = 0; i < n; i++) 
       s.insert(arr[i]);
  
    for (int i = 0; i < n; i++) 
    {
       auto it = s.find(arr[i]);
       it++;
       if (it != s.end())           
          cout << *it << " ";       
       else
          cout << "_ ";
     }
}
  
// Driver code
int main()
{
    int ar[] = { 6, 3, 9, 8, 10, 2, 1, 15, 7 };
    int n = sizeof(ar) / sizeof(ar[0]);
    smallestGreater(ar, n);
    return 0;
}

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Output :

7 6 10 9 15 3 2 _ 8

Time Complexity : O(n Log n). Note that self balancing search tree (implemented by set in C++) insert operations take O(Log n) time to insert and find.
Auxiliary Space: O(n)

We can also use sorting followed by binary searches to solve the above problem in same time and same auxiliary space.



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Improved By : jit_t, vt_m, manishshaw1