LeetCode 709: To Lower Case

Meta Data

#

Difficulty: easy First Attempt: 2022-08-31

• Submissions: Internal Error → Runtime Error ×3 → Accepted ×2

Approach

#

'A' to 'Z' are 65 to 90 and lowercase is exactly 32 higher. Check each character and convert uppercase ones with chr(ord(c) + 32) (String Template 4). In practice it is s.lower().

My Attempts

#

The first three wrote ord(s) (the whole string) in the condition, a TypeError for any string longer than one character, and two also lacked a closing bracket. Attempt 4 tried ord(int(i)), a ValueError on letters. Going back to ord(i) passed.

Solution

#

class Solution:
    def toLowerCase(self, s: str) -> str:
        return "".join(chr(ord(c) + 32) if "A" <= c <= "Z" else c for c in s)

Complexity

#

Time O(n), space O(n).

Mistakes to Avoid

#

• Call ord on a single character, not the whole string.

Interview Explanation

#

Uppercase letters become lowercase by adding 32 in ASCII, so I convert each character in A to Z and leave the rest. Time O(n).