LeetCode Roman to Integer
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Given a roman numeral, convert it to an integer.
Input is guaranteed to be within the range from 1 to 3999.
罗马数字定义如下:
1~9: {"I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
10~90: {"X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
100~900: {"C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
1000~3000: {"M", "MM", "MMM"}.
对罗马数字进行分析:假设I为1,那么IV,V,VI要如何表示?如果V为5,那么IV就是5-1=4,VI就是5+1=6,也就是当前面的字符a代表的数字小于后面的字符b代表的数字,那么我们就减去a所代表的数字,反之则是加上a代表的数字。(发现这个规律是解决这道题要点)
代码如下:
class Solution {public: int romanToInt(string s) { unordered_map<char,int> T = {{'I',1},{'V',5},{'X',10},{'L',50},{'C',100},{'D',500},{'M',1000}}; int result; int len = s.length(); result = T[s[len-1]]; for(int i = len-2;i>=0;i--) { if(T[s[i]] < T[s[i+1]]) result -= T[s[i]]; else result += T[s[i]]; } return result; }};
如何更快呢?
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