Implementing toLowerCase()

In programming languages that distinguish between letter cases, converting uppercase to lowercase comes down to understanding ASCII values. The key difference between corresponding uppercase and lowercase letters is 32 in ASCII encoding.

The ASCII ranges:

• Uppercase letters (A–Z): 65–90
• Lowercase letters (a–z): 97–122

Solution

class Solution {
    public String toLowerCase(String str) {
        char[] chars = str.toCharArray();
        for (int i = 0; i <= chars.length - 1; i++) {
            chars[i] = (char) ((chars[i] >= 65 && chars[i] <= 90) ? chars[i] + 32 : chars[i]);
        }
        return String.valueOf(chars);
    }
}

Complexity

• Time: O(n)
• Space: O(1)

Solves the LeetCode problem To Lower Case.