Smallest index such that there are no 0 or 1 to its right

Given a binary array of N numbers. The task is to find the smallest index such that there are either no 1’s or 0’s to the right of the index.

Note: The array will have at least one 0 and one 1.

Examples:



Input: a[] = {1, 1, 1, 0, 0, 1, 0, 1, 1}
Output: 6
At 6th index, there are no 0’s to the right of the index.

Input: a[] = {0, 1, 0, 0, 0}
Output: 1

Approach: Store the rightmost occurring index of both 1 and 0 and return the minimum of both.

Below is the implementation of the above approach:

C++

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// C++ program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to find the smallest index
// such that there are no 0 or 1 to its right
int smallestIndex(int a[], int n)
{
    // Initially
    int right1 = 0, right0 = 0;
  
    // Traverse in the array
    for (int i = 0; i < n; i++) {
  
        // Check if array element is 1
        if (a[i] == 1)
            right1 = i;
  
        // a[i] = 0
        else
            right0 = i;
    }
  
    // Return minimum of both
    return min(right1, right0);
}
// Driver code
int main()
{
  
    int a[] = { 1, 1, 1, 0, 0, 1, 0, 1, 1 };
    int n = sizeof(a) / sizeof(a[0]);
    cout << smallestIndex(a, n);
  
    return 0;
}

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Java

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// Java program to implement
// the above approach
class GFG
{
      
// Function to find the smallest index
// such that there are no 0 or 1 to its right
static int smallestIndex(int []a, int n)
{
    // Initially
    int right1 = 0, right0 = 0;
  
    // Traverse in the array
    for (int i = 0; i < n; i++) 
    {
  
        // Check if array element is 1
        if (a[i] == 1)
            right1 = i;
  
        // a[i] = 0
        else
            right0 = i;
    }
  
    // Return minimum of both
    return Math.min(right1, right0);
}
  
// Driver code
public static void main(String[] args)
{
    int []a = { 1, 1, 1, 0, 0, 1, 0, 1, 1 };
    int n = a.length;
    System.out.println(smallestIndex(a, n));
}
}
  
// This code is contributed 
// by Code_Mech.

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Python3

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# Python 3 program to implement
# the above approach
  
# Function to find the smallest 
# index such that there are no 
# 0 or 1 to its right
def smallestIndex(a, n):
      
    # Initially
    right1 = 0
    right0 = 0
  
    # Traverse in the array
    for i in range(n):
          
        # Check if array element is 1
        if (a[i] == 1):
            right1 = i
  
        # a[i] = 0
        else:
            right0 = i
  
    # Return minimum of both
    return min(right1, right0)
  
# Driver code
if __name__ == '__main__':
    a = [1, 1, 1, 0, 0, 1, 0, 1, 1]
    n = len(a)
    print(smallestIndex(a, n))
      
# This code is contributed by
# Surendra_Gangwar

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C#

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// C# program to implement
// the above approach
using System;
class GFG
{
      
// Function to find the smallest index
// such that there are no 0 or 1 to its right
static int smallestIndex(int []a, int n)
{
    // Initially
    int right1 = 0, right0 = 0;
  
    // Traverse in the array
    for (int i = 0; i < n; i++) 
    {
  
        // Check if array element is 1
        if (a[i] == 1)
            right1 = i;
  
        // a[i] = 0
        else
            right0 = i;
    }
  
    // Return minimum of both
    return Math.Min(right1, right0);
}
  
// Driver code
public static void Main()
{
    int []a = { 1, 1, 1, 0, 0, 1, 0, 1, 1 };
    int n = a.Length;
    Console.Write(smallestIndex(a, n));
}
}
  
// This code is contributed 
// by Akanksha Rai

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PHP

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<?php
// PHP program to implement
// the above approach
  
// Function to find the smallest index
// such that there are no 0 or 1 to its right
function smallestIndex($a, $n)
{
    // Initially
    $right1 = 0; $right0 = 0;
  
    // Traverse in the array
    for ($i = 0; $i < $n; $i++)
    {
  
        // Check if array element is 1
        if ($a[$i] == 1)
            $right1 = $i;
  
        // a[i] = 0
        else
            $right0 = $i;
    }
  
    // Return minimum of both
    return min($right1, $right0);
}
  
// Driver code
$a = array(1, 1, 1, 0, 0, 1, 0, 1, 1);
$n = sizeof($a);
echo smallestIndex($a, $n);
  
// This code is contributed by Akanksha Rai
?>

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Output:

6

Time Complexity: O(N)



My Personal Notes arrow_drop_up

Striver(underscore)79 at Codechef and codeforces D

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