Check if a binary string contains consecutive same or not

Given a binary string str consisting of characters ‘0’ and ‘1’. The task is to find whether the string is valid or not. A string is valid only if the characters are alternating i.e. no two consecutive characters are the same.

Examples:

Input: str[] = “010101” 
Output: Valid

Input: str[] = “010010” 
Output: Invalid 

Approach: Start traversing the string character by character and if there are any two consecutive characters that are equal then print Invalid else print Valid in the end.

Below is the implementation of the above approach: 

C++

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;

// Function that returns true is str is valid
bool isValid(string str, int len)
{

    // Assuming the string is binary
    // If any two consecutive characters are equal
    // then the string is invalid
    for (int i = 1; i < len; i++) {
        if (str[i] == str[i - 1])
            return false;
    }

    // If the string is alternating
    return true;
}

// Driver code
int main()
{
    string str = "0110";
    int len = str.length();

    if (isValid(str, len))
        cout << "Valid";
    else
        cout << "Invalid";

    return 0;
}

Java

// Java implementation of the approach
class gfg
{

// Function that returns true is str is valid
static boolean isValid(String str, int len)
{

    // Assuming the string is binary
    // If any two consecutive
    // characters are equal
    // then the string is invalid
    for (int i = 1; i < len; i++)
    {
        if (str.charAt(i) == str.charAt(i - 1))
            return false;
    }

    // If the string is alternating
    return true;
}

// Driver code
public static void main(String[] args)
{
    String str = "0110";
    int len = str.length();

    if (isValid(str, len))
        System.out.println("Valid");
    else
        System.out.println("Invalid");
}
}

// This code is Contributed by Code_Mech

Python3

# Python3 implementation of the approach

# Function that returns true is str is valid
def isValid(string, length):

    # Assuming the string is binary
    # If any two consecutive characters
    # are equal then the string is invalid
    for i in range(1, length):
        if string[i] == string[i - 1]:
            return False

    # If the string is alternating
    return True

# Driver code
if __name__ == "__main__":

    string = "0110"
    length = len(string)

    if isValid(string, length):
        print("Valid")
    else:
        print("Invalid")

# This code is contributed by Rituraj Jain

C#

// C# implementation of the approach
using System;

class gfg
{

// Function that returns true is str is valid
static bool isValid(string str, int len)
{

    // Assuming the string is binary
    // If any two consecutive
    // characters are equal
    // then the string is invalid
    for (int i = 1; i < len; i++)
    {
        if (str[i] == str[i - 1])
            return false;
    }

    // If the string is alternating
    return true;
}

// Driver code
public static void Main()
{
    string str = "0110";
    int len = str.Length;

    if (isValid(str, len))
        Console.Write("Valid");
    else
        Console.Write("Invalid");
}
}

// This code is contributed by Ita_c.

PHP

<?php
// PHP implementation of the approach

// Function that returns true is str is valid
function isValid($str, $len)
{

    // Assuming the string is binary
    // If any two consecutive characters
    // are equal then the string is invalid
    for ($i = 1; $i < $len; $i++)
    {
        if ($str[$i] == $str[$i - 1])
            return false;
    }

    // If the string is alternating
    return true;
}

// Driver code
$str = "0110";
$len = strlen($str);

if (isValid($str, $len))
    echo "Valid";
else
    echo "Invalid";

// This code is contributed by Ryuga
?>

Javascript

<script>
// Javascript implementation of the approach

// Function that returns true is str is valid
function isValid(str,len)
{
    // Assuming the string is binary
    // If any two consecutive
    // characters are equal
    // then the string is invalid
    for (let i = 1; i < len; i++)
    {
        if (str[i] == str[i - 1])
            return false;
    }

    // If the string is alternating
    return true;
}

// Driver code
let str = "0110";
let len = str.length;

if (isValid(str, len))
    document.write("Valid");
else
    document.write("Invalid");


// This code is contributed by rag2127
</script>

Output

Invalid

Time Complexity: O(N), where N is the length of the string.
Auxiliary Space: O(1), As constant extra space is used.