题解 | 最长对称子字符串

s = input()
if len(s) == 1:
    print(s)
else:
    max_len = 1
    k = 0
    
    for i in range(len(s)):
        l, r = i, i
        while l >= 0 and r < len(s) and s[l] == s[r]:
            current_len = r - l + 1
            if current_len > max_len:
                max_len = current_len
                k = l
            l -= 1
            r += 1
        
        l, r = i, i + 1
        while l >= 0 and r < len(s) and s[l] == s[r]:
            current_len = r - l + 1
            if current_len > max_len:
                max_len = current_len
                k = l
            l -= 1
            r += 1
    
    print(s[k:k + max_len])