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++

 `// C++ program to implement ` `// the above approach ` `#include ` `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; ` `} `

Java

 `// 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. `

Python3

 `# 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 `

C#

 `// 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 `

PHP

 ` `

Output:

```6
```

Time Complexity: O(N)

My Personal Notes arrow_drop_up

Striver(underscore)79 at Codechef and codeforces D

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