String Palindrome Verification

Given a string, your task is to determine if it is a palindrome considering only alphanumeric characters.

Input:

The input is a single string without any leading or trailing spaces. All characters are in lowercase.

Output:

The output should be a single line printing 'true' if the string is a palindrome, otherwise 'false'.

Example:

Input: "malayalam" Output: true Explanation: The string "malayalam" reads the same forward and backward, hence it is a palindrome.

Constraints:

0

Question

String Palindrome Verification

Given a string, your task is to determine if it is a palindrome considering only alphanumeric characters.

Input:

The input is a single string without any leading or trailing spaces. All characters are in lowercase.

Output:

The output should be a single line printing 'true' if the string is a palindrome, otherwise 'false'.

Example:

Input: "malayalam"
Output: true
Explanation: The string "malayalam" reads the same forward and backward, hence it is a palindrome.

Constraints:

0 <= N <= 10^6
N is the length of the input string.
Time Limit: 1 second

Note:

Your implementation should return a boolean value. Printing is handled internally.

Accepted Answer

We could use 2 indices (i to go from 0->n and j to go from n->0) and continously check if the character at the index i is equal to character at index j, if it is not the case, simply return false, no need to check further (as we have already found an index where the character at i isn't the same as character at j). If the string is a palindrome, we can return true at the end of the function.

Here is C++ program for the same.

#include 

using namespace std;

bool isPal(string s)
{
    int i = 0, j = s.size() - 1;
    
    while(i < j)
    {
        if(s[i] != s[j])
        {
            return false;
        }
        
        i++;
        j--;
    }
    
    return true;
}

int main()
{
    string s;
    cin>>s;
    
    if(isPal(s))
    {
        cout<<"true";
    }
    
    else
    {
        cout<<"false";
    }
    
    return 0;
}

Output of above code is:

for input "malayalam":

malayalam
true

for input "book":

book
false

for input "noon":

noon
true

Time Complexity: O(n).