Integer to Roman@leetcode

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刷题必备书籍：Cracking the Coding Interview: 150 Programming Questions and Solutions

Given an integer, convert it to a roman numeral.

Input is guaranteed to be within the range from 1 to 3999.

First of all, we need to clear of how roman numeral consist. There are corresponding number to integer in roman numeral. 

I - 1, V - 5, X - 10, L - 50, C - 100, D - 500, M - 1000.

The rule of how roman numeral forms is,

1~3 I, II, III,

4 IV,

5 V

6~8 VI, VII, VIII

9 IX

10 X

The rule of 100, 1000 are obey the consisting rule above. For example, MCMXXC = 1980, XLV = 45. 

We set a char array to put the roman elemental numeral, then we go through the number bit by bit to add the roman numeral to the string.

string intToRoman(int num)
{
   char symbol[7] = {'I', 'V', 'X', 'L', 'C', 'D', 'M'};
   int scale = 1000;
   string roman;
   for(int i =6; i>=0; i-=2)
   {
      int digit = num/scale;
      if(digit!=0)
      {
      if(digit<=3)
      {
        roman.append(digit, symbol[i]);
      }
      else if(digit == 4)
      {
         roman.append(1,symbol[i]);
         roman.append(1,symbol[i+1]);
      }
      else if(digit == 5)
      {
         roman.append(1, symbol[i+1]);
      }
      else if(digit<=8)
      {
         roman.append(1, symbol[i+1]);
         roman.append(digit-5, symbol[i]);
      }
      else if(digit == 9)
      {
         roman.append(1,symbol[i]);
         roman.append(1,symbol[i+2]);
      }
      }
      num = num%scale;
      scale/=10;
   }

   return roman;
}