LeetCode/13.roman-to-integer.cpp at master · AlienYou/LeetCode · GitHub

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/*
 * @lc app=leetcode id=13 lang=cpp
 *
 * [13] Roman to Integer
 *
 * https://leetcode.com/problems/roman-to-integer/description/
 *
 * algorithms
 * Easy (56.31%)
 * Likes:    135
 * Dislikes: 14
 * Total Accepted:    892.8K
 * Total Submissions: 1.6M
 * Testcase Example:  '"III"'
 *
 * 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, 2 is written as II in Roman numeral, just two one's added
 * together. 12 is written as XII, which is simply X + II. The number 27 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 a roman numeral, convert it to an integer.
 *
 *
 * Example 1:
 *
 *
 * Input: s = "III"
 * Output: 3
 *
 *
 * Example 2:
 *
 *
 * Input: s = "IV"
 * Output: 4
 *
 *
 * Example 3:
 *
 *
 * Input: s = "IX"
 * Output: 9
 *
 *
 * Example 4:
 *
 *
 * Input: s = "LVIII"
 * Output: 58
 * Explanation: L = 50, V= 5, III = 3.
 *
 *
 * Example 5:
 *
 *
 * Input: s = "MCMXCIV"
 * Output: 1994
 * Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
 *
 *
 *
 * Constraints:
 *
 *
 * 1 <= s.length <= 15
 * s contains only the characters ('I', 'V', 'X', 'L', 'C', 'D', 'M').
 * It is guaranteed that s is a valid roman numeral in the range [1, 3999].
 *
 */

// @lc code=start
class Solution {
public:
    int romanToInt(string s) {
        int sum = 0;
        int i;
        for (i = 0; i < s.length() - 1; ++i) {
            if (romanMap[s[i]] >= romanMap[s[i + 1]])
                sum += romanMap[s[i]];
            else
                sum -= romanMap[s[i]];
        }
        sum += romanMap[s[i]];
        return sum;
    }
private:
    unordered_map<char, int> romanMap = {
        {'I', 1},
        {'V', 5},
        {'X', 10},
        {'L', 50},
        {'C', 100},
        {'D', 500},
        {'M', 1000}
    };
};
// @lc code=end