Challenge 21 & 22 Added

Author: sahilatahar

README.md

@@ -186,6 +186,22 @@ Write a function called `isValidURL` that takes a string url as `url` in its par
 
 [Solution Explanation](./solutions/ch_20_Check_String_Url/readme.md)
 
+## Challenge 21: Validate Username
+
+Write a function that checks if a given string is a valid username. A valid username should contain only alphanumeric characters and underscores, and should be between 4 and 16 characters long.
+
+Write a function called `isValidUsername` that takes a string `username` in its parameter and returns true or false.
+
+[Solution Explanation](./solutions/ch_21_Validate_Username/readme.md)
+
+## Challenge 22: Check Leap Year
+
+Write a function that checks if a given year is a leap year.
+
+Write a function called `isLeapYear` that takes `year` in its parameter and returns true or false.
+
+[Solution Explanation](./solutions/ch_22_Check_Leap_Year/readme.md)
+
 <!-- Add new challenges before this comment -->
 
 ## Contributors

solutions/ch_21_Validate_Username/answer.js

@@ -0,0 +1,8 @@
+// Function to validate username
+function isValidUsername(username) {
+    // Regular expression pattern for username validation
+    const regex = /^[a-zA-Z0-9_]{4,16}$/;
+
+    // Test if the string matches the username pattern
+    return regex.test(username);
+}

solutions/ch_21_Validate_Username/readme.md

@@ -0,0 +1,24 @@
+# Challenge 21: Validate Username
+
+Write a function that checks if a given string is a valid username. A valid username should contain only alphanumeric characters and underscores, and should be between 4 and 16 characters long.
+
+Write a function called `isValidUsername` that takes a string `username` in its parameter and returns true or false.
+
+## Answer
+
+```javascript
+// Function to validate username
+function isValidUsername(username) {
+    // Regular expression pattern for username validation
+    const regex = /^[a-zA-Z0-9_]{4,16}$/;
+
+    // Test if the string matches the username pattern
+    return regex.test(username);
+}
+```
+
+## Answer Explanation
+
+The `isValidUsername` function takes a string as input and uses a regular expression to check if it's a valid username. The regular expression `^[a-zA-Z0-9_]{4,16}$` is used to match the username pattern.
+
+The test method is then used to check if the input string matches the regular expression, if it's a valid username function returns true otherwise false.

solutions/ch_22_Check_Leap_Year/answer.js

@@ -0,0 +1,10 @@
+// Function to check leap year
+function isLeapYear(year) {
+    // Gregorian calendar rule to check leap year
+    if ((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0) {
+        return true;
+    }
+
+    return false;
+}
+

solutions/ch_22_Check_Leap_Year/readme.md

@@ -0,0 +1,23 @@
+# Challenge 22: Check Leap Year
+
+Write a function that checks if a given year is a leap year.
+
+Write a function called `isLeapYear` that takes `year` in its parameter and returns true or false.
+
+## Answer
+
+```javascript
+// Function to check leap year
+function isLeapYear(year) {
+  // Gregorian calendar rule to check leap year
+  if ((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0) {
+    return true;
+  }
+
+  return false;
+}
+```
+
+## Answer Explanation
+
+The `isLeapYear` function takes `year` as input and check condition for leap year. if condition is satisfied returns true otherwise false.