Search insert position of K in a sorted array

Last Updated : 07 May, 2021

Given a sorted array arr[] consisting of N distinct integers and an integer K, the task is to find the index of K, if it’s present in the array arr[]. Otherwise, find the index where K must be inserted to keep the array sorted.

Examples:

Input: arr[] = {1, 3, 5, 6}, K = 5
Output: 2
Explanation: Since 5 is found at index 2 as arr[2] = 5, the output is 2.
Input: arr[] = {1, 3, 5, 6}, K = 2
Output: 1
Explanation: Since 2 is not present in the array but can be inserted at index 1 to make the array sorted.

Naive Approach: Follow the steps below to solve the problem:

Iterate over every element of the array arr[] and search for integer K.
If any array element is found to be equal to K, then print index of K.
Otherwise, if any array element is found to be greater than K, print that index as the insert position of K. If no element is found to be exceeding K, K must be inserted after the last array element.

Below is the implementation of above approach :

C++

// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find insert position of K
int find_index(int arr[], int n, int K)
{
    // Traverse the array
    for (int i = 0; i < n; i++)
 
        // If K is found
        if (arr[i] == K)
            return i;
 
        // If current array element
        // exceeds K
        else if (arr[i] > K)
            return i;
 
    // If all elements are smaller
    // than K
    return n;
}
 
// Driver Code
int main()
{
    int arr[] = { 1, 3, 5, 6 };
    int n = sizeof(arr) / sizeof(arr[0]);
    int K = 2;
    cout << find_index(arr, n, K) << endl;
    return 0;
}

Java

// Java program for the above approach
import java.io.*;
 
class GFG{
 
// Function to find insert position of K
static int find_index(int[] arr, int n, int K)
{
     
    // Traverse the array
    for(int i = 0; i < n; i++)
     
        // If K is found
        if (arr[i] == K)
            return i;
 
        // If current array element
        // exceeds K
        else if (arr[i] > K)
            return i;
 
    // If all elements are smaller
    // than K
    return n;
}
 
// Driver Code
public static void main(String[] args)
{
    int[] arr = { 1, 3, 5, 6 };
    int n = arr.length;
    int K = 2;
     
    System.out.println(find_index(arr, n, K));
}
}
 
// This code is contributed by akhilsaini

Python3

# Python program for the above approach
 
# Function to find insert position of K
def find_index(arr, n, K):
     
    # Traverse the array
    for i in range(n):
         
        # If K is found
        if arr[i] == K:
            return i
             
        # If arr[i] exceeds K
        elif arr[i] > K:
            return i
             
    # If all array elements are smaller
    return n
 
# Driver Code
arr = [1, 3, 5, 6]
n = len(arr)
K = 2
print(find_index(arr, n, K))

C#

// C# program for the above approach
using System;
 
class GFG{
 
// Function to find insert position of K
static int find_index(int[] arr, int n, int K)
{
     
    // Traverse the array
    for(int i = 0; i < n; i++)
     
        // If K is found
        if (arr[i] == K)
            return i;
 
        // If current array element
        // exceeds K
        else if (arr[i] > K)
            return i;
 
    // If all elements are smaller
    // than K
    return n;
}
 
// Driver Code
public static void Main()
{
    int[] arr = { 1, 3, 5, 6 };
    int n = arr.Length;
    int K = 2;
     
    Console.WriteLine(find_index(arr, n, K));
}
}
 
// This code is contributed by akhilsaini

Javascript

<script>
 
// Javascript program for the above approach
 
// Function to find insert position of K
function find_index(arr, n, K)
{
     
    // Traverse the array
    for(let i = 0; i < n; i++)
      
        // If K is found
        if (arr[i] == K)
            return i;
  
        // If current array element
        // exceeds K
        else if (arr[i] > K)
            return i;
  
    // If all elements are smaller
    // than K
    return n;
}
 
// Driver code
let arr = [ 1, 3, 5, 6 ];
let n = arr.length;
let K = 2;
  
document.write(find_index(arr, n, K));
 
// This code is contributed by splevel62  
 
</script>

Output:

Time Complexity: O(N)
Auxiliary Space: O(1)

Efficient Approach: To optimize the above approach, the idea is to use Binary Search. Follow the steps below to solve the problem:

Set start and end as 0 and N – 1, where the start and end variables denote the lower and upper bound of the search space respectively.
Calculate mid = (start + end) / 2.
If arr[mid] is found to be equal to K, print mid as the required answer.
If arr[mid] exceeds K, set low = mid + 1. Otherwise, set high = mid – 1.

Below is the implementation of above approach :

C++

// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find insert position of K
int find_index(int arr[], int n, int K)
{
    // Lower and upper bounds
    int start = 0;
    int end = n - 1;
 
    // Traverse the search space
    while (start <= end) {
        int mid = (start + end) / 2;
 
        // If K is found
        if (arr[mid] == K)
            return mid;
 
        else if (arr[mid] < K)
            start = mid + 1;
 
        else
            end = mid - 1;
    }
 
    // Return insert position
    return end + 1;
}
 
// Driver Code
int main()
{
    int arr[] = { 1, 3, 5, 6 };
    int n = sizeof(arr) / sizeof(arr[0]);
    int K = 2;
    cout << find_index(arr, n, K) << endl;
    return 0;
}

Java

// Java program for the above approach
import java.io.*;
 
class GFG{
 
// Function to find insert position of K
static int find_index(int[] arr, int n, int K)
{
     
    // Lower and upper bounds
    int start = 0;
    int end = n - 1;
 
    // Traverse the search space
    while (start <= end)
    {
        int mid = (start + end) / 2;
 
        // If K is found
        if (arr[mid] == K)
            return mid;
 
        else if (arr[mid] < K)
            start = mid + 1;
 
        else
            end = mid - 1;
    }
 
    // Return insert position
    return end + 1;
}
 
// Driver Code
public static void main(String[] args)
{
    int[] arr = { 1, 3, 5, 6 };
    int n = arr.length;
    int K = 2;
     
    System.out.println(find_index(arr, n, K));
}
}
 
// This code is contributed by akhilsaini

Python3

# Python program to implement
# the above approach
 
# Function to find insert position of K
def find_index(arr, n, B):
 
    # Lower and upper bounds
    start = 0
    end = n - 1
 
    # Traverse the search space
    while start<= end:
 
        mid =(start + end)//2
 
        if arr[mid] == K:
            return mid
 
        elif arr[mid] < K:
            start = mid + 1
        else:
            end = mid-1
 
    # Return the insert position
    return end + 1
 
# Driver Code
arr = [1, 3, 5, 6]
n = len(arr)
K = 2
print(find_index(arr, n, K))

C#

// C# program for the above approach
using System;
 
class GFG{
 
// Function to find insert position of K
static int find_index(int[] arr, int n, int K)
{
     
    // Lower and upper bounds
    int start = 0;
    int end = n - 1;
 
    // Traverse the search space
    while (start <= end)
    {
        int mid = (start + end) / 2;
 
        // If K is found
        if (arr[mid] == K)
            return mid;
 
        else if (arr[mid] < K)
            start = mid + 1;
 
        else
            end = mid - 1;
    }
 
    // Return insert position
    return end + 1;
}
 
// Driver Code
public static void Main()
{
    int[] arr = { 1, 3, 5, 6 };
    int n = arr.Length;
    int K = 2;
     
    Console.WriteLine(find_index(arr, n, K));
}
}
 
// This code is contributed by akhilsaini

Javascript

<script>
// JavaScript program for the above approach
 
// Function to find insert position of K
function find_index(arr, n, K)
{
    // Lower and upper bounds
    let start = 0;
    let end = n - 1;
 
    // Traverse the search space
    while (start <= end) {
        let mid = Math.floor((start + end) / 2);
 
        // If K is found
        if (arr[mid] == K)
            return mid;
 
        else if (arr[mid] < K)
            start = mid + 1;
 
        else
            end = mid - 1;
    }
 
    // Return insert position
    return end + 1;
}
 
// Driver Code
    let arr = [ 1, 3, 5, 6 ];
    let n = arr.length;
    let K = 2;
    document.write(find_index(arr, n, K) + "<br>");
 
 
 
 
// This code is contributed by Surbhi Tyagi.
</script>

Output:

Time Complexity: O(log N)
Auxiliary Space: O(1)

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