java算法面试题及答案

以下是几个Java算法面试题及答案，供参考：

1. 逆序输出字符串

public static void reverseString(String str) {
    if (str == null || str.length() <= 1) {
        System.out.println(str);
    } else {
        System.out.print(str.charAt(str.length()-1));
        reverseString(str.substring(0, str.length()-1));
    }
}

2. 查找数组中的最大值和次大值

public static void findMaxAndSecondMax(int[] arr) {
    int max = Integer.MIN_VALUE;
    int secondMax = Integer.MIN_VALUE;
    for (int i = 0; i < arr.length; i++) {
        if (arr[i] > max) {
            secondMax = max;
            max = arr[i];
        } else if (arr[i] > secondMax && arr[i] != max) {
            secondMax = arr[i];
        }
    }
    System.out.println("Max: " + max);
    System.out.println("Second Max: " + secondMax);
}

3. 链表反转

class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}

public static ListNode reverseList(ListNode head) {
    ListNode prev = null;
    ListNode curr = head;
    while (curr != null) {
        ListNode nextTemp = curr.next;
        curr.next = prev;
        prev = curr;
        curr = nextTemp;
    }
    return prev;
}

4. 判断字符串是否为回文字符串

public static boolean isPalindrome(String s) {
    s = s.replaceAll("[^a-zA-Z0-9]", "").toLowerCase();
    for (int i = 0; i < s.length() / 2; i++) {
        if (s.charAt(i) != s.charAt(s.length() - 1 - i)) {
            return false;
        }
    }
    return true;
}