Given a lowercase English string *s*, determine whether *s* is a pangram (contains every letter 'a' to 'z' at least once). Return `true` if it is a pangram, otherwise `false`.
s = "string to check"
boolean (true/false)
Example 1:
Input:
s = "thequickbrownfoxjumpsoverthelazydog"
Output:
true
Explanation:
The string contains every letter 'a' to 'z'.
Example 2:
Input:
s = "leetcode"
Output:
false
Explanation:
Letters such as 'a', 'b', 'c' are missing, so it is not a pangram.