12.integer-to-roman.cpp

/*
 * [12] Integer to Roman
 *
 * https://leetcode.com/problems/integer-to-roman/description/
 *
 * algorithms
 * Medium (46.43%)
 * Total Accepted:    143.4K
 * Total Submissions: 308.7K
 * Testcase Example:  '3'
 *
 * Roman numerals are represented by seven different symbols: I, V, X, L, C, D
 * and M.
 * 
 * 
 * Symbol       Value
 * I             1
 * V             5
 * X             10
 * L             50
 * C             100
 * D             500
 * M             1000
 * 
 * For example, two is written as II in Roman numeral, just two one's added
 * together. Twelve is written as, XII, which is simply X + II. The number
 * twenty seven is written as XXVII, which is XX + V + II.
 * 
 * Roman numerals are usually written largest to smallest from left to right.
 * However, the numeral for four is not IIII. Instead, the number four is
 * written as IV. Because the one is before the five we subtract it making
 * four. The same principle applies to the number nine, which is written as IX.
 * There are six instances where subtraction is used:
 * 
 * 
 * I can be placed before V (5) and X (10) to make 4 and 9. 
 * X can be placed before L (50) and C (100) to make 40 and 90. 
 * C can be placed before D (500) and M (1000) to make 400 and 900.
 * 
 * 
 * Given an integer, convert it to a roman numeral. Input is guaranteed to be
 * within the range from 1 to 3999.
 * 
 * Example 1:
 * 
 * 
 * Input: 3
 * Output: "III"
 * 
 * Example 2:
 * 
 * 
 * Input: 4
 * Output: "IV"
 * 
 * Example 3:
 * 
 * 
 * Input: 9
 * Output: "IX"
 * 
 * Example 4:
 * 
 * 
 * Input: 58
 * Output: "LVIII"
 * Explanation: C = 100, L = 50, XXX = 30 and III = 3.
 * 
 * 
 * Example 5:
 * 
 * 
 * Input: 1994
 * Output: "MCMXCIV"
 * Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
 * 
 */
class Solution {
public:
    string intToRoman(int num) {
	vector<vector<string>> v(4);
	v[0] = {"I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
	v[1] = {"X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
	v[2] = {"C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
	v[3] = {"M", "MM", "MMM"};
	string ans;
	int t = 0;
	while (num) {
		if (num%10) ans = v[t][num%10-1] + ans;
		num /= 10;
		t++;
	}
	return ans;       
    }
};