oj回文子串

# 给你一个字符串a和一个正整数n,
# 判断a中是否存在长度为n的回文子串。
# 如果存在，则输出YES，否则输出NO。
# 回文串的定义：记串str逆序之后的字符串是str1，
# 若str=str1,则称str是回文串，如"abcba".


def huiwen(a, n):
    newA = ''
    for i in range(n // 2):
        newA += a[i]

    mid = (n // 2) + 1
    behindA = a[mid:]

    behindAR = behindA[:: -1]

    if newA == behindAR:
        # print(behindAR)
        return 'YES'
    else:
        return 'NO'


if __name__ == '__main__':
    a = input('a:')
    n = int(input('n:'))

    if n == 1:
        print('YES')
    else:
        finish = n
        flag = 0
        for i in range(0, len(a) - n + 1):
            strA = a[i: finish]
            # print(newA)
            finish += 1

            result = huiwen(strA, n)
            if result == 'YES':
                flag = 1
                break
            else:
                flag = 0

        if flag == 1:
            print('YES')
        else:
            print('NO')