Create Roman_to_Integer.cpp

Roman_to_Integer.cpp

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+/*
+Given a roman numeral, convert it to an integer
+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, 2 is written as II in Roman numeral, just two ones added together.
+12 is written as XII, which is simply X + II. 
+The number 27 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.
+Expected Time Complexity: O(|s|), |s| = length of string s.
+Expected Auxiliary Space: O(1)
+*/
+
+#include<iostream>
+#include<map>
+using namespace std;
+
+
+int romanToInt(string s) {
+    map<char, int> roman;
+    roman.insert(make_pair('I',1));
+    roman.insert(make_pair('V',5));
+    roman.insert(make_pair('X',10));
+    roman.insert(make_pair('L',50));
+    roman.insert(make_pair('C',100));
+    roman.insert(make_pair('D',500));
+    roman.insert(make_pair('M',1000));
+    int len=s.length(), num, sum=0;
+    for(int i=0; i<len; )
+    {
+        if(i==(len-1) || (roman[s[i]] >= roman[s[i+1]]))
+        {
+            num=roman[s[i]];
+            i++;
+        }
+        else
+        {
+        num=roman[s[i+1]]-roman[s[i]];
+        i=i+2;
+        }
+        sum =sum +num;
+    }
+    return sum;
+}
+
+int main()
+{
+    string s;
+    cout<<"Enter a Roman Number: ";
+    cin>>s;                       // input should be in the form Roman numericals (Upper case) [I, V, X, L, C, D and M]
+    int result;
+    result=romanToInt(s);
+    cout<<result;
+    return 0;
+}