通过重新排列给定字符串的字符来获得最大的罗马数字

#include <bits/stdc++.h>
using namespace std;
// function to create the value of Roman characters if the character is not present in Roman then return -1
int romanVal(char ch){
   if (ch == 'I'){
      return 1;
   }
   else if (ch == 'X'){
      return 10;
   }
   else if (ch == 'V'){
      return 5;
   }
   else if (ch == 'D'){
      return 500;
   }
   else if(ch == 'C'){
      return 100;
   }
   else if(ch == 'L'){
      return 50;
   }
   else if(ch == 'M'){
      return 1000;
   }
   else{
      // given number is invalid 
      return -1;
   }
}
// function to get the decimal value from the given Roman value 
int romanToDec(string str){
   int ans = 0; // variable to store the final answer 
   int len = str.size(); // length of the final string 	
   ans = romanVal(str[len - 1]); // initializing the value of result variable
   // Traversing over the given string
   for (int i = len - 2; i>= 0; i--){
      if (romanVal(str[i]) <romanVal(str[i + 1])){
      ans -= romanVal(str[i]);
      }
      else{
      ans += romanVal(str[i]);
      }
   }
   return ans; // return the final answer 
}
// function for converting the decimal value to roman 
string decToRoman(int num){
   string ans = ""; // variable to store the final answer 
   // array to store all the numeric values that can be represented in the roman 
   int decVals[] = {1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000};
   // array to store all the roman values that equivalent to the given decimal values  
   string romVals[] = { "I", "IV", "V", "IX", "X", "XL", "L", "XC", "C", "CD" , "D", "CM", "M" };
   int idx = 12; // starting from the last index 
   while (num> 0){
      int cur = num / decVals[idx];
      num = num % decVals[idx];
      while (cur--) {
         ans += romVals[idx];
      }
      idx--;
   }
   return ans; // return the final answer 
}
// compare function to sort the string in the decreasing order
bool cmp(char a, char b){
   // getting values of both the current characters 
   int val_a = romanVal(a);
   int val_b = romanVal(b);
   return (val_a>val_b);
}
// creating function to find the largest possible result
string findString(string str){	
   // traversing over the string to check if any invalid character is present or not 
   for(int i=0; i<str.length(); i++){
      if(romanVal(str[i]) == -1){
         // if romalValue is -1 means chracter is invalid 
         return "Invalid";
      }
   }
   sort(str.begin(), str.end(), cmp);
   int num = romanToDec(str);
   string rom = decToRoman(num);
   if (str != rom){
      return "Invalid";
   }
   return rom; // returning the result 
}
int main(){
   string str = "VICML"; // given string 
   cout << "Given String: " << str << endl;	
   cout << "Largest Roman Numeral possible by rearranging characters of a given string: ";
   // calling to the function 
   cout<<findString(str)<<endl;
   return 0;
}