12.integer-to-roman.java

/*
 * @lc app=leetcode id=12 lang=java
 *
 * [12] Integer to Roman
 *
 * https://leetcode.com/problems/integer-to-roman/description/
 *
 * algorithms
 * Medium (52.19%)
 * Likes:    913
 * Dislikes: 2483
 * Total Accepted:    326.8K
 * Total Submissions: 605.6K
 * 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: L = 50, V = 5, III = 3.
 * 
 * 
 * Example 5:
 * 
 * 
 * Input: 1994
 * Output: "MCMXCIV"
 * Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
 * 
 */

// @lc code=start
class Solution {
    public String intToRoman(int num) {
        StringBuffer buf = new StringBuffer();
        int[] keys = { 1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000 };
        String[] values = { "I", "IV", "V", "IX", "X", "XL", "L", "XC", "C", "CD", "D", "CM", "M" };
        for (int i = keys.length - 1; i >= 0; i--) {
            while (num >= keys[i]) {
                num -= keys[i];
                buf.append(values[i]);
            }
        }
        return buf.toString();
    }
}
// @lc code=end