题目

Seven different symbols represent Roman numerals with the following values:

Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules:

If the value does not start with 4 or 9, select the symbol of the maximal value that can be subtracted from the input, append that symbol to the result, subtract its value, and convert the remainder to a Roman numeral. If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol, for example, 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV), 9 (IX), 40 (XL), 90 (XC), 400 (CD) and 900 (CM). Only powers of 10 (I, X, C, M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V), 50 (L), or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form. Given an integer, convert it to a Roman numeral.

思路

大模拟，不必多说，直接上答案

code

class Solution {
public:
    string intToRoman(int num) {
        string input=to_string(num);
        reverse(input.begin(),input.end());
        while(input.size()<4) input.push_back('0');
        reverse(input.begin(),input.end());
        string res;

        char half[4]={'x','D','L','V'};
        char full[4]={'M','C','X','I'};
        for(int j=0;j<4;j++){
            if(input[j]=='9'){
                res+=full[j];
                res+=full[j-1];
            }
            else if(input[j]>='5'){
                res+=half[j];
                for(char i='5';i<input[j];i++){
                    res+=full[j];
                }
            }
            else if(input[j]=='4'){
                res+=full[j];
                res+=half[j];
            }
            else {
                for(char i='0';i<input[j];i++){
                    res+=full[j];
                }
            }
        }
        return res;
    }
};