LeetCode 13. Roman to Integer

题目描述

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.

题目思路

代码 C++

• 思路一、
  1，前一个字符比后一个字符大，则前一个字符数值直接累加
  2，前一个字符比后一个字符小，则后一个字符数值减去前一个字符数值

class Solution {
public:
    int romanToInt(string s) {
        map mp={{'I',1}, {'V', 5},{'X', 10}, {'L', 50},{'C',100}, {'D',500}, {'M',1000}};
        int result = 0;
        int i = 0;
        while(i < s.size()){
            if(mp[s[i]] < mp[s[i+1]]){
                result = result + mp[s[i+1]] - mp[s[i]];
                i = i + 2;
            }
            else{
                result = result + mp[s[i]];
                i = i + 1;
            }       
        }
        return result;
    }
};

总结展望

• 发现大厂字符串考察的挺多的啊
• 做春招笔试题发现自己字符串不行，今天开始补补吧