LC520 Detect Capital

# main idea, compare based on case 
# time O(O) spaceO(1)
class Solution:
    def detectCapitalUse(self, word: str) -> bool:
        up = string.ascii_uppercase
        low = string.ascii_lowercase 
        def helper(word,standard):
            for each in word:
                if each not in standard:
                    return False
            return True
        if word[0] in low and word[-1] in low:
            return helper(word,low)
        elif word[0] in up and word[-1]:
            word = word[1:]
            return helper(word,up) or helper(word,low)
        else: return False

class Solution:
    def detectCapitalUse(self, word: str) -> bool:
        n = len(word)
        i = 0
        cap = False
        if word[0].isupper():
            cap = True
        cnt_low = 0
        while i < n:
            if i == 0:
                cap = word[i].isupper()
            if word[i].islower():
                cnt_low += 1
            i += 1
        return (cap and cnt_low == n-1) or (cnt_low == n) or (cap and cnt_low == 0)

class Solution:
    # main idea regex, combine case 2([A-Z]*) and case 3[A-Z][a-z]* ==> .[a-z]*
    # time O(N) but highly rely on pattern and implementaion ;  space O(1)
    def detectCapitalUse(self, word: str) -> bool:
        return re.fullmatch(r"[A-Z]*|.[a-z]*",word)