回文数

判断一个整数是否是回文数。回文数是指正序（从左向右）和倒序（从右向左）读都是一样的整数。

如果输入是负数：return false;

输入正数：如121, return true;

第一遍写法直接判断数字第一位和最后一位是否相等：

class Solution {
public:
    bool isPalindrome(int x) {
        if(x <0) return false;
        int bits = 0;
        int t = x;
        while(t) {
            t = t / 10;
            bits += 1;
        }
        int left = x;
        int right = x;
        for(int i = 1; i <= bits/2; i++){
            cout << int(left / pow(10, bits-i)) << "," <<  right %10<< endl;
            if ( int(left / pow(10, bits-i)) != right %10 ){
               // cout << left / pow(10, bits-i) << "," << right%10 << endl;
                return false;
            } else {
                left -= int(left/(pow(10, bits-i))) * pow(10,bits-i);
                right = right /10;
            }
        }
        return true;   
    }
};

然后发现有更简单的代码：

class Solution {
public:
    bool isPalindrome(int x) {
        if(x <0) return false;
        //int bits = 0;
        long int ret = 0;
        int t = x;
        while(t != 0) {
            ret = ret*10 + t%10;
            t = t/10;
        }
        return ret == x;

    }
};