Roman to Integer
Signals to notice
Brute force first
Map each symbol, add values left to right — misses subtraction cases. That instinct is useful because it follows the prompt literally, but it usually keeps revisiting work the problem is begging you to organize.
The key insight
If current symbol < next symbol, subtract instead of add. The goal is not to be clever for its own sake, but to remember the one relationship that keeps the solution grounded as you move forward.
What must stay true
When a smaller value appears before a larger one, subtract it (IV = 4, not 6). If that remains true after every update, the rest of the reasoning has a stable place to stand.
Easy way to go wrong
Not handling the subtraction rule — compare each symbol with the next one. When the code becomes mechanical before the idea is clear, small edge cases start breaking the whole story.