Roman to Integer(罗马数转为整数)leetcode13

Dear 丶 2022-05-24 04:41 160阅读 0赞

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: C = 100, L = 50, XXX = 30 and III = 3.

Example 5:

Input: "MCMXCIV"
    Output: 1994
    Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

code1：

public int romanToInt(String s) {
            /*int[] nums={1000,900,500,400,100,90,50,40,10,9,5,4,1};
            String[] romans={"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};
            int count=0;
            int result=0;
            while(count<s.length()){
                String res1="";
                if(count<s.length()-1)
                    res1=s.substring(count,count+2);
                String res2=s.substring(count,count+1);
                for(int i=0;i<romans.length;i++){
                    if(romans[i].equals(res1)){
                        count+=2;
                        result+=nums[i];
                        break;
                    }else if(romans[i].equals(res2)){
                        count++;
                        result+=nums[i];
                        break;
                    }
                }
                
            }
            return result;
    }

code2：

public int romanToInt(String s) {
            int nums[]=new int[s.length()];
        for(int i=0;i<s.length();i++){
            switch (s.charAt(i)){
                case 'M':
                    nums[i]=1000;
                    break;
                case 'D':
                    nums[i]=500;
                    break;
                case 'C':
                    nums[i]=100;
                    break;
                case 'L':
                    nums[i]=50;
                    break;
                case 'X' :
                    nums[i]=10;
                    break;
                case 'V':
                    nums[i]=5;
                    break;
                case 'I':
                    nums[i]=1;
                    break;
            }
        }
        /*int sum=0;//从前往后遍历或者下面那种从后往前遍历
        for(int i=0;i<nums.length-1;i++){
            if(nums[i]<nums[i+1])
                sum-=nums[i];
            else
                sum+=nums[i];
        }
        return sum+nums[nums.length-1];*/
            int sum=nums[nums.length-1];
            for(int i=nums.length-2;i>=0;i--){
                if(nums[i]<nums[i+1])
                    sum-=nums[i];
                else
                    sum+=nums[i];
            }
            return sum;
        }