【LeetCode】12. Integer to Roman (2 solutions)

Integer to Roman

Given an integer, convert it to a roman numeral.

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

逐区间做处理。

解法一：非递归

class Solution {
public:
    string intToRoman(int num) {
        string ret;
        //M<-->1000
        while(num >= )
        {
            ret += 'M';
            num -= ;
        }
        //to here, num < 1000
        //CM<-->900
        if(num >= )
        {
            ret += "CM";
            num -= ;
        }
        //to here, num < 900
        //D<-->500
        if(num >= )
        {
            ret += 'D';
            num -= ;
        }
        //to here, num < 500
        if(num >= )
        {
            ret += "CD";
            num -= ;
        }
        //to here, num < 400
        //C<-->100
        while(num >= )
        {
            ret += 'C';
            num -= ;
        }
        //to here, num < 100
        //XC<-->90
        if(num >= )
        {
            ret += "XC";
            num -= ;
        }
        //to here, num < 90
        //L<-->50
        if(num >= )
        {
            ret += 'L';
            num -= ;
        }
        //to here, num < 50
        //XL<-->40
        if(num >= )
        {
            ret += "XL";
            num -= ;
        }
        //to here, num < 40
        //X<-->10
        while(num >= )
        {
            ret += 'X';
            num -= ;
        }
        //to here, num < 10
        //IX<-->9
        if(num >= )
        {
            ret += "IX";
            num -= ;
        }
        //to here, num < 9
        //V<-->5
        if(num >= )
        {
            ret += 'V';
            num -= ;
        }
        //to here, num < 5
        //IV<-->4
        if(num >= )
        {
            ret += "IV";
            num -= ;
        }
        //to here, num < 4
        //I<-->1
        while(num >= )
        {
            ret += 'I';
            num -= ;
        }
        return ret;
    }
};

解法二：递归

class Solution {
public:
    string intToRoman(int num) {
        if(num >= )
            return "M" + intToRoman(num-);
        else if(num >= )
            return "CM" + intToRoman(num-);
        else if(num >= )
            return "D" + intToRoman(num-);
        else if(num >= )
            return "CD" + intToRoman(num-);
        else if(num >= )
            return "C" + intToRoman(num-);
        else if(num >= )
            return "XC" + intToRoman(num-);
        else if(num >= )
            return "L" + intToRoman(num-);
        else if(num >= )
            return "XL" + intToRoman(num-);
        else if(num >= )
            return "X" + intToRoman(num-);
        else if(num >= )
            return "IX" + intToRoman(num-);
        else if(num >= )
            return "V" + intToRoman(num-);
        else if(num >= )
            return "IV" + intToRoman(num-);
        else if(num >= )
            return "I" + intToRoman(num-);
        else
            return "";
    }
};