13.roman-to-integer.go

/*
 * @lc app=leetcode id=13 lang=golang
 *
 * [13] Roman to Integer
 *
 * https://leetcode.com/problems/roman-to-integer/description/
 *
 * algorithms
 * Easy (55.37%)
 * Likes:    2325
 * Dislikes: 3578
 * Total Accepted:    724.6K
 * Total Submissions: 1.3M
 * 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, 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 a roman numeral, convert it to an integer. Input is guaranteed to be
 * within the range from 1 to 3999.
 *
 * Example 1:
 *
 *
 * Input: "III"
 * Output: 3
 *
 * Example 2:
 *
 *
 * Input: "IV"
 * Output: 4
 *
 * Example 3:
 *
 *
 * Input: "IX"
 * Output: 9
 *
 * Example 4:
 *
 *
 * Input: "LVIII"
 * Output: 58
 * Explanation: L = 50, V= 5, III = 3.
 *
 *
 * Example 5:
 *
 *
 * Input: "MCMXCIV"
 * Output: 1994
 * Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
 *
 */

// @lc code=start
func romanToInt(s string) int {
	return romanToInt2(s)
}

// cmp s[i] < s[i+1]
func romanToInt2(s string) int {
	if len(s) == 0 {
		return 0
	}

	hash := map[byte]int{'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
	retVal := 0
	for i := 0; i < len(s); i++ {
		if i != len(s)-1 && hash[s[i]] < hash[s[i+1]] {
			retVal -= hash[s[i]]
		} else {
			retVal += hash[s[i]]
		}
	}
	return retVal
}

func romanToInt1(s string) int {
	if len(s) == 0 {
		return 0
	}

	hash := map[byte]int{'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
	retVal := 0
	for i := 0; i < len(s); {
		if i == len(s)-1 {
			retVal += hash[s[i]]
			i++
		} else {
			// forward next 2
			if hash[s[i]] < hash[s[i+1]] {
				retVal += hash[s[i+1]] - hash[s[i]]
				i = i + 2
			} else {
				retVal += hash[s[i]]
				i++
			}
		}
	}
	return retVal
}

// @lc code=end