13 - Roman to Integer

 JAVA

• class Solution {
      public int romanToInt(String s) {
          String cs = "IVXLCDM";
          int[] vs = {1, 5, 10, 50, 100, 500, 1000};
          Map<Character, Integer> d = new HashMap<>();
          for (int i = 0; i < vs.length; ++i) {
              d.put(cs.charAt(i), vs[i]);
          }
          int n = s.length();
          int ans = d.get(s.charAt(n - 1));
          for (int i = 0; i < n - 1; ++i) {
              int sign = d.get(s.charAt(i)) < d.get(s.charAt(i + 1)) ? -1 : 1;
              ans += sign * d.get(s.charAt(i));
          }
          return ans;
      }
  }

C++

• class Solution {
  public:
      int romanToInt(string s) {
          unordered_map<char, int> nums{
              {'I', 1},
              {'V', 5},
              {'X', 10},
              {'L', 50},
              {'C', 100},
              {'D', 500},
              {'M', 1000},
          };
          int ans = nums[s.back()];
          for (int i = 0; i < s.size() - 1; ++i) {
              int sign = nums[s[i]] < nums[s[i + 1]] ? -1 : 1;
              ans += sign * nums[s[i]];
          }
          return ans;
      }
  };