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:    http://leetcode.com/problems/integer-to-roman/

题解：

数值计算的题目，需要了解罗马数字的规律。  Time Complexity - O(n)， Space Complexity - O(n)

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();
    }
}

二刷:

I, IV, V, IX, X, XL, L, XC, C, CD, D, CM, M分别代表 1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000

Java:

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

Python: 

class Solution(object):
    def intToRoman(self, num):
        """
        :type num: int
        :rtype: str
        """
        romans = ["M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"]
        numbers = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1]
        res = ''
        for i in range(0, len(romans)):
            while num >= numbers[i]:
                num -= numbers[i]
                res += romans[i]
        return res

三刷:

Java:

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

Reference:

https://leetcode.com/discuss/49870/my-java-solution-easy-to-understand