Leetcode 题目摘录

Easy

9. Palindrome Number
   Given an integer x, return true if x is palindrome integer.
   An integer is a palindrome when it reads the same backward as forward.
   For example, 121 is a palindrome while 123 is not.

class Solution {
public:
    bool isPalindrome(int x) {
        if(x<0|| (x!=0 &&x%10==0)) return false; //ends with 0
        int sum=0;
        while(x>sum)
        {
            sum = sum*10+x%10;
            x = x/10;
        }
        return (x==sum)||(x==sum/10);  //when x contains only one digit
    }
};

13. Roman to Integer

int romanToInt(string s) 
{
    unordered_map<char, int> T = { { 'I' , 1 },
                                   { 'V' , 5 },
                                   { 'X' , 10 },
                                   { 'L' , 50 },
                                   { 'C' , 100 },
                                   { 'D' , 500 },
                                   { 'M' , 1000 } };
                                   
   int sum = T[s.back()];
   for (int i = s.length() - 2; i >= 0; --i) 
   {
       if (T[s[i]] < T[s[i + 1]])
       {
           sum -= T[s[i]];
       }
       else
       {
           sum += T[s[i]];
       }
   }
   
   return sum;
}