Integer to Roman

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Given an integer, convert it to a roman numeral.

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

罗马数字有如下符号：

基本字符IVXLCDM对应阿拉伯数字1510501005001000

计数规则：

相同的数字连写，所表示的数等于这些数字相加得到的数，例如：III = 3
小的数字在大的数字右边，所表示的数等于这些数字相加得到的数，例如：VIII = 8
小的数字，限于（I、X和C）在大的数字左边，所表示的数等于大数减去小数所得的数，例如：IV = 4
正常使用时，连续的数字重复不得超过三次
在一个数的上面画横线，表示这个数扩大1000倍（本题只考虑3999以内的数，所以用不到这条规

思路 1 ：从后往前遍历，遇到一样的就粘贴上。 i = i + 2; num = num / 10;

思路2 ：只有4,9是左减，其余的数字都是右加。所以，构建两个数组，分别是数字和对应的字母。数字，要把所有的4，9加进来。包括4，9，40，90，400，900. 从前往后，用取余的方法来进位，num %= base[i];

public class Solution {    public String intToRoman(int num) {        if(num <= 0 || num >= 4000)            return null;                    String roman[] = { "I","V","X","L","C","D","M" };        String RomanString = "";        int i = 0;        while(num != 0)        {            int temp = num % 10;            String Rstr = "";            switch(temp)            {                case 1:                    Rstr = roman[i];                    break;                case 2:                    Rstr = roman[i] + roman[i];                    break;                case 3:                    Rstr = roman[i] + roman[i] + roman[i];                    break;                case 4:                    Rstr = roman[i] + roman[i+1];                    break;                case 5:                    Rstr = roman[i+1];                    break;                case 6:                    Rstr = roman[i+1] + roman[i];                    break;                case 7:                    Rstr = roman[i+1] + roman[i] + roman[i];                    break;                case 8:                    Rstr = roman[i+1] + roman[i] + roman[i] + roman[i];                    break;                case 9:                    Rstr = roman[i] + roman[i+2];                    break;            }            RomanString = Rstr + RomanString;            i = i + 2;            num = num / 10;        }        return RomanString;    }}

public class Solution {    public String intToRoman(int num) {        int[] base = { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 };String[] roman = { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X","IX", "V", "IV", "I" };String result = "";for (int i = 0; num > 0; i++) {int count = num / base[i];num %= base[i];while (count > 0) {result += roman[i];--count;}}return result;    }}

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