Roman to Integer

Problem

Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

Related Topics:

Math String

Analysis

通过观察,可以发现,每位上,49 是特别的,例如:IV(4)IX(9)4 可以看成是 -1 + 59 则是 -1 + 10,所以将每个罗马字符对应的数字进行累加即可(当前一个字符比后一个字符小,则看成负数相加)。

Code

class Solution {

    private val map = mapOf(
            'M' to 1000,
            'D' to 500,
            'C' to 100,
            'L' to 50,
            'X' to 10,
            'V' to 5,
            'I' to 1)

    fun romanToInt(s: String): Int {

        var num = 0
        var pre = 0
        for (i in s) {
            num += if (pre < map[i]!!) -pre else pre
            pre = map[i]!!
        }

        return num + pre
    }
}

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