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Repeatedly search an element by doubling it after every successful search
  • Difficulty Level : Easy
  • Last Updated : 15 Mar, 2019

Given an array “a[]” and integer “b”. Find whether b is present in a[] or not. If present, then double the value of b and search again. We repeat these steps until b is not found. Finally we return value of b.

Examples:

Input : a[] = {1, 2, 3}
          b = 1 
Output :4
Initially we start with b = 1. Since 
it is present in array, it becomes 2.
Now 2 is also present in array b becomes 4 .
Since 4 is not present, we return 4.

Input : a[] = {1 3 5 2 12}
          b = 3 
Output :6

Question Source : Asked in Yatra.com Online Test

1) Sort the input array.
2) Keep doing binary search and doubling until the element is not present.



The below code using binary_search() in STL

C++




// C++ program to repeatedly search an element by
// doubling it after every successful search
#include <bits/stdc++.h>
using namespace std;
  
int findElement(int a[], int n, int b)
{
    // Sort the given array so that binary search
    // can be applied on it
    sort(a, a + n);
  
    int max = a[n - 1]; // Maximum array element
  
    while (b < max) {
  
        // search for the element b present or
        // not in array
        if (binary_search(a, a + n, b))
            b *= 2;
        else
            return b;
    }
  
    return b;
}
  
// Driver code
int main()
{
    int a[] = { 1, 2, 3 };
    int n = sizeof(a) / sizeof(a[0]);
    int b = 1;
    cout << findElement(a, n, b);
    return 0;
}

Java




// Java program to repeatedly search an element by
// doubling it after every successful search
import java.util.Arrays;
public class Test4 {
  
    static int findElement(int a[], int n, int b)
    {
        // Sort the given array so that binary search
        // can be applied on it
        Arrays.sort(a);
  
        int max = a[n - 1]; // Maximum array element
  
        while (b < max) {
  
            // search for the element b present or
            // not in array
            if (Arrays.binarySearch(a, b) > -1)
                b *= 2;
            else
                return b;
        }
  
        return b;
    }
  
    // Driver code
    public static void main(String args[])
    {
        int a[] = { 1, 2, 3 };
        int n = a.length;
        int b = 1;
        System.out.println(findElement(a, n, b));
    }
}
// This article is contributed by Sumit Ghosh

Python




# Python program to repeatedly search an element by
# doubling it after every successful search
  
def binary_search(a, x, lo = 0, hi = None):
    if hi is None:
        hi = len(a)
    while lo < hi:
        mid = (lo + hi)//2
        midval = a[mid]
        if midval < x:
            lo = mid + 1
        elif midval > x: 
            hi = mid
        else:
            return mid
    return -1
  
def findElement(a, n, b):
     
    # Sort the given array so that binary search
    # can be applied on it
    a.sort()
   
    mx = a[n - 1] # Maximum array element
   
    while (b < max):
          
        # search for the element b present or
        # not in array
        if (binary_search(a, b, 0, n) != -1):
            b *= 2
        else:
            return b
    return b
   
# Driver code
a = [ 1, 2, 3 ]
n = len(a)
b = 1
print findElement(a, n, b)
  
# This code is contributed by Sachin Bisht

C#




// C# program to repeatedly search an
// element by doubling it after every
// successful search
using System;
  
public class GFG {
  
    static int findElement(int[] a,
                           int n, int b)
    {
  
        // Sort the given array so that
        // binary search can be applied
        // on it
        Array.Sort(a);
  
        // Maximum array element
        int max = a[n - 1];
  
        while (b < max) {
  
            // search for the element b
            // present or not in array
            if (Array.BinarySearch(a, b) > -1)
                b *= 2;
            else
                return b;
        }
  
        return b;
    }
  
    // Driver code
    public static void Main()
    {
        int[] a = { 1, 2, 3 };
        int n = a.Length;
        int b = 1;
        Console.WriteLine(findElement(a, n, b));
    }
}
  
// This code is contributed by vt_m.

PHP




<?php
// Php program to repeatedly search an element by
// doubling it after every successful search
  
function binary_search($a, $x, $lo=0, $hi=NULL)
{
    if ($hi == NULL)
        $hi = count($a);
    while ($lo < $hi) {
        $mid = ($lo + $hi) / 2;
        $midval = $a[$mid];
        if ($midval < $x)
            $lo = $mid + 1;
        else if ($midval > $x)
            $hi = $mid;
        else
            return $mid;
    }
    return -1;
}
  
function findElement($a, $n, $b)
{
// Sort the given array so that binary search
// can be applied on it
    sort($a);
  
    $mx = $a[$n - 1]; // Maximum array element
  
while ($b < max($a)) {
  
// search for the element b present or
// not in array
    if (binary_search($a, $b, 0, $n) != -1)
        $b *= 2;
    else
        return $b;
}
return $b;
}
  
// Driver code
$a = array(1, 2, 3 );
$n = count($a);
$b = 1;
echo findElement($a, $n, $b);
  
// This code is contributed by Srathore
?> 


Output:
4

This article is contributed by Karan Kumar Gautam. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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