[Java Interview Manual - Algorithms] Given an integer array, please judge whether it is a palindrome array?

For a given array A[] composed of positive integers, if the arrangement of the numbers after A is reversed is exactly the same as that of A, then the array A is a palindrome. For example [1, 2, 3, 2, 1] is a palindrome, but [1, 2, 3, 4] is not a palindrome.

To determine whether an array is a palindrome, there are usually the following implementation ideas:

• Two-way traversal from end to end to determine whether the elements of the array are the same;
• Reverse the entire array, and judge whether the reversed array elements are the same as the original array elements one by one;

Example 1 - end-to-end bidirectional traversal :

 private static boolean isPalindrome(int[] array) {
        for (int start = 0, end = array.length - 1; start < end; start++, end--) {
            if (array[start] != array[end]) {
                return false;
            }
        }

        return true;
    }

Or use a while loop to achieve

 private static boolean isPalindrome(int[] array) {
        int start = 0;
        int end = array.length - 1;
        while (start < end) {
            if (array[start] != array[end]) {
                return false;
            }
            start++;
            end--;
        }

        return true;
    }

Example 2 - Reverse array :

 private static boolean isPalindrome(int[] array) {
        int[] reversedArray = new int[array.length];
        for (int i = array.length - 1; i >= 0; i--) {
            reversedArray[array.length - 1 - i] = array[i];
        }

        for (int i = 0; i < array.length; i++) {
            if (array[i] != reversedArray[i]) {
                return false;
            }
        }

        return true;
    }

Test verification

 public static void main(String[] args) {
        System.out.println(isPalindrome(new int[]{1, 2, 3, 2, 1}));
        System.out.println(isPalindrome(new int[]{1, 2, 3, 4}));
    }

The output is as follows:

true
false

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