数值问题（需要考虑最大、最小等边界问题）

9. Palindrome Number

Determine whether an integer is a palindrome. Do this without extra space.
代码如下：

class Solution {
public:
    bool isPalindrome(int x) {
        if(x<0)
          return false;
        int temp = x;
        int t = 0;
        long long sum = 0;
        
        while(x)
        {
            t = x%10;
            sum = 10*sum + t;
            x = x/10;
        }
        if(sum<INT_MIN||sum>INT_MAX)
                return false;
        
        return sum == temp;
    }
};

7. Reverse Integer

Reverse digits of an integer.

Example1: x = 123, return 321
Example2: x = -123, return -321

class Solution {
public:
    int reverse(int x) {
        int n = 0;
        long long sum = 0;
        while(x)
        {
            n = x%10;
            sum = 10*sum + n;
            x = x/10;
        }
        if(sum<INT_MIN||sum>INT_MAX)
        {
            sum = sum>0 ? INT_MAX:INT_MIN;
            return 0;
        }
        return sum;
    }
};

8. String to Integer (atoi)

Implement atoi to convert a string to an integer.

class Solution {
public:
    int myAtoi(string str) {
        int flag = 1;
        int i = 0,n = str.size();
        if(n<=0)
          return 0;
        while(i<n&&str[i]==' ')
        {
            i++;
        }
        if(str[i]=='+')
        {
            i++;
        }
        else if(str[i]=='-')
        {
            flag = -1;
            i++;
        }
        long long sum = 0;
        while(i<n)
        {
            if(str[i]>='0'&&str[i]<='9')
              sum = 10*sum + str[i] - '0';
            else
              return (int)(flag*sum);
              
            if(sum>INT_MAX||sum<INT_MIN)
              return flag>0 ? INT_MAX:INT_MIN;
            i++;
        }
        return (int)(flag*sum);
    }
};