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Roman To Integer (Leetcode Problem #13)
Java Solution for https://leetcode.com/problems/roman-to-integer/
Published in
3 min readSep 9, 2021
Youtube Video
If you prefer video format : https://youtu.be/BC-mHuUAaZA
Understanding Problem
- Find the enitre problem here : https://leetcode.com/problems/roman-to-integer/
- We have been given roman symbols with its value and we need to convert roman numeral to integer value.
input_x = "LVIII"
output_x = 58
L = 50; V=5; III=3 - There some facts about roman numerals. They are usually written from largest to smallest. In above example L is larger than V.
- There some instances mentioned below where subtraction is used.
- I can be placed before (V & X); X can be placed before (L & C); C can be placed before (D & M).
- So four is not written lie IIII , rather it is written as IV.
My Thought About Solution
- I can convert roman numeral string to char array.
- Since generally roman numerals are written largest to smallest usually except some cases where subtraction is needed, I can just check the case that if current char value is greater than next char value, if yes than i can just add the value of it to my sum.
- But if i have case where current roman numeral value is less than next roman value then i have to subtract it. For example if roman numeral is “IV”, in that case if my current char is I then sum = sum- Value of (I) due to subtraction rule of roman numerals
- Data structure: We need hashmap to store roman numerals and its corrosponding value
Time-complexity: O(length(N)) where N is the input roman numeral
Space-complexity: Constant Space since roman numerals are constant in time
Pseudocode
1: Convert Input roman numeral to char array
2: Create Map of each roman numeral char and its corrosponding value
3: Traverse input char array
4: for each char array calculate
a: if current roman numeral value is greater than next roman
numeral - value then add the value of current roman numeral
to the total sum 
