Merge pull request #4 from hirentimbadiya/hirentimbadiya

Palindrome number - Intermediate javascript problem for issue#2

Author: devvsakib

0001 Palindrome ( L - I)/README.md

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+# Palindrome (L-I)
+
+## Problem
+- Write a function in JavaScript that takes an integer as input and returns a boolean value indicating whether the number is a palindrome or not.
+
+- A palindrome number is a number that remains the same when its digits are reversed. For example, 121, 1221, 12321 are all palindrome numbers. The function should return true if the given number is a palindrome, and false otherwise.
+
+- The function should be able to handle negative numbers and should not convert the number to a string or array. Instead, it should perform the check by manipulating the number directly.
+
+- Example Inputs and Outputs:
+
+- Input: 121 -> Output: true
+- Input: -121 -> Output: false
+- Input: 10 -> Output: false
+- Input: 12321 -> Output: true
+
+## Solution
+
+```javascript
+let n = 12321;
+
+if(palindrome(n)){
+    console.log( n + " is a Palindrome number");
+}else{
+    console.log( n + " is not a Palindrome number");
+}
+
+/* function to check if a number is palindrome or not 
+by reversing the number and comparing it with the original number */
+function palindrome(n){
+    // create a temp variable to store the value of n
+    let temp = n;
+    // create a variable to store the reverse of n
+    let rev = 0;
+    // reverse the number
+    while(temp > 0){
+        let lastDigit = temp % 10;
+        rev = rev * 10 + lastDigit;
+        temp = Math.floor(temp / 10);
+    }
+    // check if the reverse is equal to n
+    return rev == n;
+}
+
+// using two pointers
+function palindromeTwoPointer(n){
+    // convert the number to string
+    let str = n.toString();
+     // if the number is negative, remove the negative sign from the string
+     if (str[0] === '-') {
+        return false;
+    }
+    // create two pointers
+    let start = 0;
+    let end = str.length - 1;
+    // loop through the string
+    while(start < end){
+        // check if the characters at the two pointers are equal
+        if(str[start] != str[end]){
+            return false;
+        }
+        // increment start and decrement end
+        start++;
+        end--;
+    }
+    return true;
+}
+```
+
+## How it works
+### First Approach :
+- Create a variable temp to store the value of n for later use.
+- Create a variable rev to store the reverse of n. rev is initially set to 0.
+- Use a while loop to reverse the number n. The loop continues as long as temp is greater than 0.
+-   a. In each iteration, the last digit of temp is calculated by taking the remainder when temp is divided by 10.
+    b. The last digit is then added to rev by multiplying rev by 10 and adding the last digit.
+    c. The value of temp is then updated by dividing it by 10 and flooring the result. This discards the last digit of temp.
+- After the while loop, the function checks if the reversed number rev is equal to the original number n.
+- If rev is equal to n, the function returns true, indicating that n is a palindrome. Otherwise, the function returns false.
+
+### Second Approach : 
+- First, the number is converted to a string.
+- If the first character of the string is a negative sign (-), the function returns false as negative numbers cannot be palindromes.
+- Two pointers are created, start and end, and initialized to the first and last characters of the string, respectively.
+- The function then enters a loop, which continues as long as start is less than end.
+- Within the loop, the characters at the start and end pointers are compared. If they are not equal, the function returns false as the number is not a palindrome.
+- If the characters are equal, start is incremented and end is decremented, and the loop continues.
+- When the loop is finished, the function returns true, indicating that the number is a palindrome.
+
+
+## References
+- [Wikipedia](https://en.wikipedia.org/wiki/Palindromic_number#)
+
+
+## Problem Added By
+- [GitHub](https://www.github.com/hirentimbadiya) 
+- [LinkedIn](https://www.linkedin.com/in/hirentimbadiya74)
+- [Twitter](https://twitter.com/heyhiru)
+
+
+## Contributing
+Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.
+
+Please make sure to update tests as appropriate.

0001 Palindrome ( L - I)/palindrome.js

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+let n = -12321;
+
+if(palindrome(n)){
+    console.log( n + " is a Palindrome number");
+}else{
+    console.log( n + " is not a Palindrome number");
+}
+
+/* function to check if a number is palindrome or not 
+by reversing the number and comparing it with the original number */
+function palindrome(n){
+    // create a temp variable to store the value of n
+    let temp = n;
+    // create a variable to store the reverse of n
+    let rev = 0;
+    // reverse the number
+    while(temp > 0){
+        let lastDigit = temp % 10;
+        rev = rev * 10 + lastDigit;
+        temp = Math.floor(temp / 10);
+    }
+    // check if the reverse is equal to n
+    return rev == n;
+}
+
+// using two pointers
+function palindromeTwoPointer(n){
+    // convert the number to string
+    let str = n.toString();
+     // if the number is negative, remove the negative sign from the string
+     if (str[0] === '-') {
+        return false;
+    }
+    // create two pointers
+    let start = 0;
+    let end = str.length - 1;
+    // loop through the string
+    while(start < end){
+        // check if the characters at the two pointers are equal
+        if(str[start] != str[end]){
+            return false;
+        }
+        // increment start and decrement end
+        start++;
+        end--;
+    }
+    return true;
+}