leetcode:Roman to Integer and Integer to Roman
2015-06-03
罗马数字以前接触过I到VIII比较多,直到遇见这个题目才知道更详细。阿拉伯数字和罗马数字之间的转换最重的是了解罗马数字的规则。
罗马数字规则:(总结)
1, 罗马数字共有7个,即I(1)、V(5)、X(10)、L(50)、C(100)、D(500)和M(1000)。
罗马数字中没有“0”。
2, 重复次数:一个罗马数字最多重复3次。
3, 右加左减:
在较大的罗马数字的右边记上较小的罗马数字,表示大数字加小数字。
在较大的罗马数字的左边记上较小的罗马数字,表示大数字减小数字。
4, 左减的数字有限制,仅限于I、X、C,且放在大数的左边只能用一个。
(*) V 和 X 左边的小数字只能用Ⅰ。
(*) L 和 C 左边的小数字只能用X。
(*) D 和 M 左 边的小数字只能用C。
Roman to integer
Given a roman numeral,convert it to an integer.Input is guaranteed to be within the range from 1 to 3999.
两种 C++ solution
1、
class Solution { public: int romanToInt(string s) { int res=0; int lastValue=0; int digit; for(int i=s.size()-1;i>=0;i--){ switch(s[i]){ case 'I': digit=1; break; case 'V': digit=5; break; case 'X': digit=10; break; case 'L': digit=50; break; case 'C': digit=100; break; case 'D': digit=500; break; case 'M': digit=1000; break; } if(digit>=lastValue){ res+=digit; lastValue=digit; } else res-=digit; } return res; } };
或: Problem is simpler to solve by working the string from back to front and using a map. Runtime speed is 56 ms.
2、
class Solution { public: int romanToInt(string s) { unordered_map<char, int> T = { { 'I' , 1 }, { 'V' , 5 }, { 'X' , 10 }, { 'L' , 50 }, { 'C' , 100 }, { 'D' , 500 }, { 'M' , 1000 } }; int sum = T[s.back()]; for (int i = s.length() - 2; i >= 0; --i) { if (T[s[i]] < T[s[i + 1]]) { sum -= T[s[i]]; } else { sum += T[s[i]]; } } return sum; } };
Integer to Roman
Given an integer,convert it to a roman numeral.Input is guaranteed tobe within the range from 1 to 3999.
1、16ms c++ solution
class Solution { public: const static string THOUS[]; const static string HUNDS[]; const static string TENS[]; const static string ONES[]; string intToRoman(int num) { string result; result += THOUS[(int)(num/1000)%10]; result += HUNDS[(int)(num/100)%10]; result += TENS[(int)(num/10)%10]; result += ONES[num%10]; return result; } }; const string Solution::THOUS[] = {"","M","MM","MMM"}; const string Solution::HUNDS[] = {"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"}; const string Solution::TENS[] = {"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"}; const string Solution::ONES[] = {"","I","II","III","IV","V","VI","VII","VIII","IX"};
2、 44ms c++ solution
class Solution { public: string intToRoman(int num) { vector<pair<string, int> > mp { {"M", 1000}, {"CM", 900}, {"D", 500}, {"CD", 400}, {"C", 100}, {"XC", 90}, {"L", 50}, {"XL", 40}, {"X", 10}, {"IX", 9}, {"V", 5}, {"IV", 4}, {"I", 1} }; string result; while (num) { for (auto p : mp) { if (num >= p.second) { result += p.first, num -= p.second; break; } } } return result; } };