LeetCode Online Judge 题目C# 练习 - Integer to Roman
Given an integer, convert it to a roman numeral.
Input is guaranteed to be within the range from 1 to 3999.
1 static string[] D1 = { "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX" }; 2 static string[] D10 = { "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC" }; 3 static string[] D100 = { "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM" }; 4 static string[] D1000 = { "M", "MM", "MMM" }; 5 public static string IntegertoRoman(int num) 6 { 7 string ret = ""; 8 int[] arr = new int[4]; 9 //Fill in array 1976 -> arr[0] = 6, arr[1] = 7, arr[2] = 9 and arr[3] = 1 10 for (int i = 0; i <= 3; i++) 11 { 12 arr[i] = num % (int)Math.Pow(10, i + 1) / (int)Math.Pow(10, i); 13 } 14 15 //Fill in ret ret = "M" + "CM" + "LXX" + "VI"; 16 for (int i = 3; i >= 0; i--) 17 { 18 if (arr[i] != 0) 19 { 20 if (i == 3) 21 ret += D1000[arr[i] - 1]; 22 if (i == 2) 23 ret += D100[arr[i] - 1]; 24 if (i == 1) 25 ret += D10[arr[i] - 1]; 26 if (i == 0) 27 ret += D1[arr[i] - 1]; 28 } 29 } 30 31 return ret; 32 }
代码分析：
可以先问面试官可不可以建这个look up table。如果可以，那这样做就快， 狠， 准了。
1 public static string IntegertoRoman2(int num) 2 { 3 StringBuilder ret = new StringBuilder(); 4 int[] arr = new int[4]; 5 //Fill in array 1976 -> arr[0] = 6, arr[1] = 7, arr[2] = 9 and arr[3] = 1 6 for (int i = 0; i <= 3; i++) 7 { 8 arr[i] = num % (int)Math.Pow(10, i + 1) / (int)Math.Pow(10, i); 9 } 10 11 ret.Append(IntegertoRoman2Helper(arr[3], 3)); 12 ret.Append(IntegertoRoman2Helper(arr[2], 2)); 13 ret.Append(IntegertoRoman2Helper(arr[1], 1)); 14 ret.Append(IntegertoRoman2Helper(arr[0], 0)); 15 16 return ret.ToString(); 17 } 18 19 public static string IntegertoRoman2Helper(int num, int level) 20 { 21 string[] map = new string[] { "I", "V", "X", "L", "C", "D", "M" }; 22 string s1 = null, s2 = null, s3 = null; 23 24 if (level == 0) 25 { 26 s1 = "I"; s2 = "V"; s3 = "X"; 27 } 28 else if (level == 1) 29 { 30 s1 = "X"; s2 = "L"; s3 = "C"; 31 } 32 else if (level == 2) 33 { 34 s1 = "C"; s2 = "D"; s3 = "M"; 35 } 36 else if (level == 3) 37 { 38 s1 = "M"; 39 } 40 41 StringBuilder sb = new StringBuilder(); 42 43 if (num >= 1 && num <= 3) 44 { 45 for (int i = 1; i <= num; i++) 46 sb.Append(s1); 47 } 48 else if (num == 4) 49 { 50 sb.Append(s1 + s2); 51 } 52 else if (num >= 5 && num <= 8) 53 { 54 sb.Append(s2); 55 for (int i = 1; i <= num - 5; i++) 56 sb.Append(s1); 57 } 58 else if (num == 9) 59 sb.Append(s1 + s3); 60 61 return sb.ToString(); 62 }
代码分析：
以上代码是没有用look up table的。稍微麻烦一点。
做个笔记，在C++中如果想用StringBuilder(所谓的SB), 可以用std::stringstream, Append 字符串 就是 ss << "abc" << "def";
