kth smallest/largest in a small range unsorted array
Last Updated :
07 Sep, 2022
Find kth smallest or largest element in an unsorted array, where k<=size of array. It is given that elements of array are in small range.
Examples:
Input : arr[] = {3, 2, 9, 5, 7, 11, 13}
k = 5
Output: 9
Input : arr[] = {16, 8, 9, 21, 43}
k = 3
Output: 16
Input : arr[] = {50, 50, 40}
k = 2
Output: 50
As the given array elements are in a small range, we can direct the index table to do something similar to counting sort. We store counts of elements, then we traverse the count array and print k-th element.
Implementation: Following is the implementation of the above algorithm
C++
// C++ program of kth smallest/largest in
// a small range unsorted array
#include <bits/stdc++.h>
using namespace std;
#define maxs 1000001
int kthSmallestLargest(int* arr, int n, int k)
{
int max_val = *max_element(arr, arr+n);
int hash[max_val+1] = { 0 };
// Storing counts of elements
for (int i = 0; i < n; i++)
hash[arr[i]]++;
// Traverse hash array build above until
// we reach k-th smallest element.
int count = 0;
for (int i=0; i <= max_val; i++)
{
while (hash[i] > 0)
{
count++;
if (count == k)
return i;
hash[i]--;
}
}
return -1;
}
int main()
{
int arr[] = { 11, 6, 2, 9, 4, 3, 16 };
int n = sizeof(arr) / sizeof(arr[0]), k = 3;
cout << "kth smallest number is: "
<< kthSmallestLargest(arr, n, k) << endl;
return 0;
}
// Java program of kth smallest/largest in
// a small range unsorted array
import java.util.Arrays;
class GFG
{
static int maxs = 1000001;
static int kthSmallestLargest(int[] arr, int n, int k)
{
int max_val = Arrays.stream(arr).max().getAsInt();
int hash[] = new int[max_val + 1];
// Storing counts of elements
for (int i = 0; i < n; i++)
{
hash[arr[i]]++;
}
// Traverse hash array build above until
// we reach k-th smallest element.
int count = 0;
for (int i = 0; i <= max_val; i++)
{
while (hash[i] > 0)
{
count++;
if (count == k)
{
return i;
}
hash[i]--;
}
}
return -1;
}
// Driver code
public static void main(String[] args)
{
int arr[] = {11, 6, 2, 9, 4, 3, 16};
int n = arr.length, k = 3;
System.out.println("kth smallest number is: "
+ kthSmallestLargest(arr, n, k));
}
}
// This code has been contributed by 29AjayKumar
# Python 3 program of kth smallest/largest
# in a small range unsorted array
def kthSmallestLargest(arr, n, k):
max_val = arr[0]
for i in range(len(arr)):
if (arr[i] > max_val):
max_val = arr[i]
hash = [0 for i in range(max_val + 1)]
# Storing counts of elements
for i in range(n):
hash[arr[i]] += 1
# Traverse hash array build above until
# we reach k-th smallest element.
count = 0
for i in range(max_val + 1):
while (hash[i] > 0):
count += 1
if (count == k):
return i
hash[i] -= 1
return -1
# Driver Code
if __name__ == '__main__':
arr = [11, 6, 2, 9, 4, 3, 16]
n = len(arr)
k = 3
print("kth smallest number is:",
kthSmallestLargest(arr, n, k))
# This code is contributed by
# Surendra_Gangwar
// C# program of kth smallest/largest in
// a small range unsorted array
using System;
using System.Linq;
class GFG
{
static int maxs = 1000001;
static int kthSmallestLargest(int[] arr, int n, int k)
{
int max_val = arr.Max();
int []hash = new int[max_val + 1];
// Storing counts of elements
for (int i = 0; i < n; i++)
{
hash[arr[i]]++;
}
// Traverse hash array build above until
// we reach k-th smallest element.
int count = 0;
for (int i = 0; i <= max_val; i++)
{
while (hash[i] > 0)
{
count++;
if (count == k)
{
return i;
}
hash[i]--;
}
}
return -1;
}
// Driver code
public static void Main()
{
int []arr = {11, 6, 2, 9, 4, 3, 16};
int n = arr.Length, k = 3;
Console.WriteLine("kth smallest number is: "
+ kthSmallestLargest(arr, n, k));
}
}
/* This code contributed by PrinciRaj1992 */
<?php
// PHP program of kth smallest/largest in
// a small range unsorted array
$maxs = 1000001;
function kthSmallestLargest(&$arr, $n, $k)
{
global $maxs;
$max_val = max($arr);
$hash = array_fill(0,$max_val+1, NULL);
// Storing counts of elements
for ($i = 0; $i < $n; $i++)
$hash[$arr[$i]]++;
// Traverse hash array build above until
// we reach k-th smallest element.
$count = 0;
for ($i=0; $i <= $max_val; $i++)
{
while ($hash[$i] > 0)
{
$count++;
if ($count == $k)
return $i;
$hash[$i]--;
}
}
return -1;
}
$arr = array ( 11, 6, 2, 9, 4, 3, 16 );
$n = sizeof($arr) / sizeof($arr[0]);
$k = 3;
echo "kth smallest number is: "
. kthSmallestLargest($arr, $n, $k)."\n";
return 0;
?>
<script>
// Javascript program of kth smallest/largest in
// a small range unsorted array
let maxs = 1000001;
function kthSmallestLargest(arr,n,k)
{
let max_val = Math.max(...arr);
let hash = new Array(max_val + 1);
for(let i=0;i<hash.length;i++)
{
hash[i]=0;
}
// Storing counts of elements
for (let i = 0; i < n; i++)
{
hash[arr[i]]++;
}
// Traverse hash array build above until
// we reach k-th smallest element.
let count = 0;
for (let i = 0; i <= max_val; i++)
{
while (hash[i] > 0)
{
count++;
if (count == k)
{
return i;
}
hash[i]--;
}
}
return -1;
}
// Driver code
let arr=[11, 6, 2, 9, 4, 3, 16];
let n = arr.length, k = 3;
document.write("kth smallest number is: "
+ kthSmallestLargest(arr, n, k));
// This code is contributed by avanitrachhadiya2155
</script>
Outputkth smallest number is: 4
Complexity Analysis:
- Time Complexity: O(n + max_val)
- Auxiliary Space: O(n) for hash array.
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