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Find the missing number in a sorted array of limited range
  • Difficulty Level : Basic
  • Last Updated : 29 Apr, 2021

Given a sorted array of size n and given that there are numbers from 1 to n+1 with one missing, the missing number is to be found. It may be assumed that array has distinct elements.
Examples: 

Input : 1 3 4 5 6
Output : 2

Input  : 1 2 3 4 5 7 8 9 10
Output  : 6

We traverse all elements. For every element a[i], we check if it is equal to i+1 or not. If not, we return (i+1). 

C++




// C++ program to find missing Number in
// a sorted array of size n and distinct
// elements.
#include<bits/stdc++.h>
using namespace std;
 
// Function to find missing number
int getMissingNo(int a[], int n)
{
    for (int i=0; i<n; i++)       
        if (a[i] != (i+1))
            return (i+1);
  
    // If all numbers from 1 to n
    // are present
    return n+1;
}
 
// Driver code
int main()
{
    int a[] = {1, 2, 4, 5, 6};
    int n = sizeof(a) / sizeof(a[0]);
    cout << getMissingNo(a, n);
    return 0;
}
 
// This code is contributed by Sachin Bisht

Java




// Java program to find missing Number in
// a sorted array of size n and distinct
// elements.
class Main
{
    // Function to find missing number
    static int getMissingNo(int a[])
    {
        int n = a.length;
        for (int i=0; i<n; i++)       
            if (a[i] != (i+1))
                return (i+1);
 
        // If all numbers from 1 to n
        // are present
        return n+1;
    }
       
    /* program to test above function */
    public static void main(String args[])
    {
        int a[] = {1, 2, 4, 5, 6};
        System.out.println(getMissingNo(a));
    }
}

Python




# Python program to find missing Number in
# a sorted array of size n and distinct
# elements.
 
# function to find missing number
def getMissingNo(a):
    n = len(a)
     
    for i in range(n):
        if(a[i] != i + 1):
            return i + 1
             
    # If all numbers from 1 to n
    # are present
    return n+1
 
# Driver code
a = [1, 2, 4, 5, 6]
print(getMissingNo(a))
 
# This code is contributed by Sachin Bisht

C#




// C# program to find missing Number
// in a sorted array of size n and
// distinct elements.
using System;
 
class GFG
{
     
// Function to find missing number
static int getMissingNo(int []a, int n)
{
    for (int i = 0; i < n; i++)
        if (a[i] != (i + 1))
            return (i + 1);
 
    // If all numbers from
    // 1 to n are present
    return n + 1;
}
 
// Driver code
public static void Main()
{
    int []a = {1, 2, 4, 5, 6};
    int n = a.Length;
    Console.WriteLine(getMissingNo(a, n));
}
}
 
// This code is contributed by ihritik

PHP




<?php
// PHP program to find missing Number
// in a sorted array of size n and
// distinct elements.
 
// Function to find missing number
function getMissingNo($a, $n)
{
    for ($i = 0; $i < $n; $i++)
        if ($a[$i] != ($i + 1))
            return ($i + 1);
 
    // If all numbers from
    // 1 to n are present
    return $n + 1;
}
 
// Driver code
$a = array(1, 2, 4, 5, 6);
$n = sizeof($a);
echo getMissingNo($a, $n);
 
// This code is contributed
// by ihritik
?>

Javascript




<script>
// javascipt program to find missing Number
// in a sorted array of size n and
// distinct elements.
     
// Function to find missing number
function getMissingNo(a,n)
{
    for (let i = 0; i < n; i++)
        if (a[i] != (i + 1))
            return (i + 1);
 
    // If all numbers from
    // 1 to n are present
    return n + 1;
}
 
// Driver code
let a = [1, 2, 4, 5, 6]
let n = a.length;
document.write(getMissingNo(a, n));
 
// This code is contributed by mohit kumar 29.
</script>

Output : 

3

Time Complexity: O(n)

Auxiliary Space: O(1)
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