def isPalindrome(s):
    '''
    驗證迴文串很簡單 雙指標
    但是字串查找回文串比較難
    '''
    strs = ''
    if s =='':  ###定義空字元是迴文串
        return True
    for i in s:
        if i.isdigit():
            strs += i
        if i.isalpha():
            strs += i.lower()
        else:
            continue
    print(strs)
    n = len(strs)
    l,r = 0,n-1
    while l <= r:
        if strs[l] == strs[r]:
            l += 1
            r -= 1
        else:
            return False
    return True




s = "A man, a plan, a canal: Panama"
isPalindrome(s)