[LeetCode] Palindrome Number

Determine whether an integer is a palindrome. Do this without extra space.

Some hints:

Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

思路：每次判断数字的最高位和最低位，如果相等将数字丢弃最高位和最低位后继续比较

使用len保存数字最高位的表示

class Solution {
public:
    bool isPalindrome(int x) {
        if (x < 0 || ((x != 0) && (x % 10 == 0)))
            return false;
        int len = 1;
        while (x / len >= 10) 
            len *= 10;
        while (x > 0) {
            int lo = x % 10;
            int hi = x / len;
            if (lo != hi)
                return false;
            else {
                x = (x % len) / 10;
                len /= 100;
            }
        }
        return true;
    }
};
// 145 ms