To Lower Case
(#709), Easy
Category: String
Problem Statement
You're given a string `s`. You need to return the same string, but with every uppercase letter converted to lowercase. All other characters remain unchanged.
Examples
Input: "Hello"
Output: "hello"
Explanation: Only 'H' is uppercase and gets converted.
Input: "here"
Output: "here"
Explanation: All characters are already lowercase.
Input: "LOVELY"
Output: "lovely"
Explanation: All uppercase letters are converted to lowercase.
Approach
Manual ASCII Conversion
- Initialize an empty string `str` to build the lowercase result.
- Loop through each character in the input string `s`.
- Check if the character is uppercase (ASCII between 65 and 90).
- If yes, convert it to lowercase by adding 32 to its ASCII code.
- Use `String.fromCharCode()` to convert the code back to a character.
- Append the converted character to `str`, or append the original character if not uppercase.
- Return the final string after the loop.
var toLowerCase = function (s) {
let str = "";
for (let i = 0; i < s.length; i++) {
let charCode = s[i].charCodeAt(0);
if (charCode >= 65 && charCode <= 90) {
str += String.fromCharCode(charCode + 32);
} else {
str += s[i];
}
}
return str;
};One-Liner Built-In Method
- Use the built-in `toLowerCase()` method to convert the entire string.
var toLowerCase = function (s) {
return s.toLowerCase();
};Complexity
Time: O(n), where n is the length of the string.
Space: O(n), for the result string.