Problem

Given a string s, return a new string containing only the alphabetic characters of s (a–z, A–Z), in their original order. Digits, spaces, punctuation and other symbols are dropped.

Input / Output

• Input: string s.
• Output: filtered string.

Examples

Example 1 Input: s = "He11o, W0rld!" Output: "HeoWrld"

Example 2 Input: s = "123 456" Output: ""

Example 3 Input: s = "abc" Output: "abc"

Constraints

• 0 <= s.length <= 10^5

Approach

Single pass; keep a character if it is a letter. Two ways to test:

• isalpha() / Character.isLetter — Unicode-aware, accepts accented letters.
• Range check 'a' <= c <= 'z' or 'A' <= c <= 'Z' — ASCII only, what most such problems intend.

Use a builder/list and join once; repeated string concatenation is quadratic in immutable-string languages.

This is the filtering half of "Valid Palindrome" (LeetCode 125), where you strip non-alphanumerics and lowercase before comparing — knowing this problem makes that one a two-liner.

Complexity

• Time: O(n)
• Space: O(n) for the output.

Reference solution (Python)

def only_alphabets(s: str) -> str:
    return ''.join(c for c in s if ('a' <= c <= 'z') or ('A' <= c <= 'Z'))

Test cases

Input	Expected
"He11o, W0rld!"	"HeoWrld"
"123 456"	""
"abc"	"abc"
"a-b_c"	"abc"