[leet code] 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.

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Analysis:

2 key points:

1. The match between roman numeral and int:

I = 1

V = 5

X = 10

L = 50

C = 100

D = 500

M = 1000

In order the deal with the "append left" cases (e.g. 4 = IX, 40 = XL, etc.), we extend the matches as follow: (the most simplest method I could find to deal with these cases)

IV = 4

IX = 9

XL = 40

XC = 90

CD = 400

CM = 900

2. Use StringBuffer to store the result string (dynamic length), and return by .toString() method.

public class Solution {    public String intToRoman(int num) {        if(num == 0) return null;                StringBuffer sb = new StringBuffer();            int numM = num/1000;            if(numM > 0){                num -= numM*1000;                for (int i=1; i<=numM; i++) sb.append('M');            }            int numCM = num/900;            if(numCM > 0){                num -= numCM*900;                for (int i=1; i<=numCM; i++) sb.append("CM");            }                         int numD = num/500;            if(numD > 0){                num -= numD*500;                for (int i=1; i<=numD; i++) sb.append('D');            }             int numCD = num/400;            if(numCD > 0){                num -= numCD*400;                for (int i=1; i<=numCD; i++) sb.append("CD");            }                         int numC = num/100;            if(numC>0){                num -= numC*100;                for (int i=1; i<=numC; i++) sb.append('C');            }             int numXC = num/90;            if(numXC>0){                num -= numXC*90;                for (int i=1; i<=numXC; i++) sb.append("XC");            }                         int numL = num/50;            if(numL>0){                num -= numL*50;                for (int i=1; i<=numL; i++) sb.append('L');            }                         int numXL = num/40;            if(numXL>0){                num -= numXL*40;                for (int i=1; i<=numXL; i++) sb.append("XL");            }                         int numX = num/10;            if(numX>0){                num -= numX*10;                for (int i=1; i<=numX; i++) sb.append('X');            }             int numIX = num/9;            if(numIX>0){                num -= numIX*10;                for (int i=1; i<=numIX; i++) sb.append("IX");            }                        int numV = num/5;            if(numV>0){                num -= numV*5;                for (int i=1; i<=numV; i++) sb.append('V');            }                         int numIV = num/4;            if(numIV>0){                num -= numIV*4;                for (int i=1; i<=numIV; i++) sb.append("IV");            }                         int numI = num;            if(numI>0){                for (int i=1; i<=numI; i++) sb.append('I');            }                         return sb.toString();    }}

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