12. Integer to Roman

题目：

Given an integer, convert it to a roman numeral.

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

链接：https://leetcode.com/problems/integer-to-roman/#/description

4/9/2017

18%, 115ms

public class Solution {
    public String intToRoman(int num) {
        HashMap<Integer, Character> hm = new HashMap<Integer, Character>();
        StringBuilder sb = new StringBuilder();
        hm.put(1, 'I');
        hm.put(5, 'V');
        hm.put(10, 'X');
        hm.put(50, 'L');
        hm.put(100, 'C');
        hm.put(500, 'D');
        hm.put(1000, 'M');

        while (num > 0) {
            if (num / 1000 != 0) {
                int count = num / 1000;
                num -= 1000 * count;
                while (count > 0) {
                    sb.append(hm.get(1000));
                    count--;
                }
            } else if (num / 900 != 0) {
                sb.append(hm.get(100));
                sb.append(hm.get(1000));
                num -= 900;
            } else if (num / 500 != 0) {
                sb.append(hm.get(500));
                num -= 500;
            } else if (num / 400 != 0) {
                sb.append(hm.get(100));
                sb.append(hm.get(500));
                num -= 400;
            } else if (num / 100 != 0) {
                int count = num / 100;
                num -= 100 * count;
                while (count > 0) {
                    sb.append(hm.get(100));
                    count--;
                }
            } else if (num / 90 != 0) {
                sb.append(hm.get(10));
                sb.append(hm.get(100));
                num -= 90;
            } else if (num / 50 != 0) {
                sb.append(hm.get(50));
                num -= 50;
            } else if (num / 40 != 0) {
                sb.append(hm.get(10));
                sb.append(hm.get(50));
                num -= 40;
            } else if (num / 10 != 0) {
                int count = num / 10;
                num -= 10 * count;
                while (count > 0) {
                    sb.append(hm.get(10));
                    count--;
                }
            } else if (num / 9 != 0) {
                sb.append(hm.get(1));
                sb.append(hm.get(10));
                num -= 9;
            } else if (num / 5 != 0) {
                sb.append(hm.get(5));
                num -= 5;
            } else if (num / 4 != 0) {
                sb.append(hm.get(1));
                sb.append(hm.get(5));
                num -= 4;
            } else {
                while (num > 0) {
                    sb.append(hm.get(1));
                    num--;
                }
            }
        }
        return sb.toString();
    }
}

其实可以多列出来很多case，比如9，4的情况。甚至可以列出来所有的例子

别人的答案：

public class Solution {
    public String intToRoman(int num) {   //Roman:   I = 1,  V = 5,   X = 10,   L = 50,   C = 100,  D = 500,  M = 1000 
        StringBuilder result = new StringBuilder();
        String [] symbol = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};    
        int [] value = {1000,900,500,400, 100, 90,  50, 40,  10, 9,   5,  4,   1};   
        for(int i = 0; num != 0; i++){
            while(num >= value[i]){
                num -= value[i];
                result.append(symbol[i]);
            }
        }
        return result.toString();
    }
}

https://discuss.leetcode.com/topic/12384/simple-solution

public static String intToRoman(int num) {
    String M[] = {"", "M", "MM", "MMM"};
    String C[] = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
    String X[] = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
    String I[] = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
    return M[num/1000] + C[(num%1000)/100] + X[(num%100)/10] + I[num%10];
}

更多讨论：https://discuss.leetcode.com/category/20/integer-to-roman