leetcode第九题--Palindrome Number

Problem:

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

click to show spoilers.

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.

老师说今天上午找我开会，等了会，也没说具体时间干脆上来刷一题。很高兴，一次就通过了。用了O（1）的空间。先将x转为相反的数，存在long long里面，然后比较这个long long 会不会和x相等。其实long也可以，因为int的最大值反过来最多也就long。如果是负数，则直接判断false。如果十以内的就直接返回true。

class Solution {

private:

//leetcode9

long long reverseInt(int x)

{

    long long result = 0;

    while(x)

    {

        result = result * 10 + x%10;

        x/=10;

    }

    return result;

}

public:

// no extra space

bool isPalindrome(int x)

{

    if (x < 0)

        return false;

    if (x < 10)

        return true;

    if (reverseInt(x) == x)

        return true;

    else

        return false;

}

};