[leetcode] 9. Palindrome Number

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1:

Input: 121
Output: true

Example 2:

Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

思路:

1 , 我的思路把数字转换为字符串.

定义两个指针,left指向字符串左边边界,right指向字符串右边边界;left和right同时向中心位置移动.直至相遇为止.如果遇到两个字符不等则说明不是回文串,直接返回false;

 public boolean isPalindrome(int x) {

        String num = String.valueOf(x);
        int l = 0, r = num.length() - 1;
        while(l < r) {
            if(num.charAt(l) != num.charAt(r)) return false;
            l++; r--;
        }
        return true;
    }
}

2, 直接把数字颠倒;

    例如, 把数字123变为321,然后判断数字是否相等; 代码以后再补上吧