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13.roman into integer

admin 11月 12, 2020 0

Question:

Given a roman numeral, convert it to an integer.

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

Hints:

Hint-1:

I - 1
V - 5
X - 10
L - 50
C - 100
D - 500
M - 1000

Hint-2:

  • If I comes before V or X, subtract 1 eg: IV = 4 and IX = 9
  • If X comes before L or C, subtract 10 eg: XL = 40 and XC = 90
  • If C comes before D or M, subtract 100 eg: CD = 400 and CM = 900

My Answer:

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class  {
    public int romanToInt(String s) {
        int len = s.length();
        
        int res = 0;
        for(int i=0;i<len;i++){
            char temp = s.charAt(i);
            switch(temp){
            case 'I':
                System.out.println(i);
                System.out.println(temp);
                if(i <= len-2 && s.charAt(i+1) == 'V'){
                    res = res + 4;
                    i = i + 1;
                    System.out.println(i);
                    System.out.println(res);
                }
                else if(i <= len-2 && s.charAt(i+1) == 'X'){
                        res = res + 9;
                        i = i + 1;
                        
                }
                else{
                    res = res + 1;
                    System.out.println(i);
                    System.out.println(res);
                }
                System.out.println(res);
                break;
            case 'V':               
                res = res + 5;
                break;
            case 'X':
                if(i <= len-2 && s.charAt(i+1) == 'L'){
                    res = res + 40;
                    i = i + 1;
                }
                else if(i <= len-2 && s.charAt(i+1) == 'C'){
                    res = res + 90;
                    i = i + 1;
                }
                else{
                    res = res + 10;
                }
                break;
            case 'L':
                res = res + 50;
                break;
            case 'C':
                if(i <= len-2 && s.charAt(i+1) == 'D'){
                    res = res + 400;
                    i = i + 1;
                }
                else if(i <= len-2 && s.charAt(i+1) == 'M'){
                    res = res + 900;
                    i = i + 1;
                }
                else{
                    res = res + 100;
                }
                break;
            case 'D':
                res = res + 500;
                break;
            case 'M':
                res = res + 1000;
                break;
            }
        }
        return res;
    }
}

I just know basic about java, so I only use sample logic.

Sorry about that.

Runtime: 300ms

Better Answers:

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class  {
    public int romanToInt(String s) {
        Map<Character, Integer> map = new HashMap<>();
        map.put('I', 1);
        map.put('V', 5);
        map.put('X', 10);
        map.put('L', 50);
        map.put('C', 100);
        map.put('D', 500);
        map.put('M', 1000);
        int len = s.length();
        int sum = map.get(s.charAt(len - 1));
        for (int i = len - 2; i >= 0; --i) {
            if (map.get(s.charAt(i)) < map.get(s.charAt(i + 1))) {
                sum -= map.get(s.charAt(i));
            } else {
                sum += map.get(s.charAt(i));
            }
        }
        return sum;
    }
}

Runtime: 149ms

Here use map HashMap, speed up~

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