leetcode 9 -- Palindrome Number

题目

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.

题意

判断给定数字是不是回文数，要求不能使用多余的空间，即不能开辟字符串来判断，而且要小心越界的情况，即不能直接逆向跟原数来比较

思路

将数字二分(若位数为奇，则不要中间位) 逆转后一部分，比较大小（可以避免越界问题）

代码

bool isPalindrome(int x) {
    int t=x;
    int i,z=0,num,sum=0;
    if(x<0)
    {
        return false;
    }
    if(x<10)
    {
        return true;
    }
    while(t)
    {
        sum++;
        t/=10;
    }
    num=sum/2;
    while(num--)
    {
        z=z*10+x%10;
        x/=10;
    }
    if(sum%2)
    {
        x/=10;
    }
    if(x==z)
    {
        return true;
    }
    else
    {
        return false;
    }
}