偶串 public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String s = scanner.nextLine(); int maxLen = 0; for (int i = 1; i < s.length() - 2; i += 2) { int newLen = (i + 1) / 2; if (s.substring(0, newLen).equals(s.substring(newLen, i + 1))) { maxLen = Math.max(maxLen, newLen); } } System.out.println(maxLen*2); scanner.close(); } 回文 public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String s = scanner.nextLine(); int[] flags = new int[26]; char[] chas = s.toCharArray(); int num = 0; for (int i = 0; i < chas.length; i++) { flags[chas[i] - 'a']++; } for (int i = 0; i < flags.length; i++) { if (flags[i] > 0 && flags[i] % 2 != 0) { num++; } } System.out.println(num); scanner.close(); }