This line defines the function romanToInt, which takes a string as input and returns an integer.

This line initializes an unordered map called romanValues , which maps each Roman numeral character to its corresponding integer value.

These lines initialize two integer variables: result, which will hold the final integer value of the Roman numeral string, and prevValue, which will hold the previous integer value encountered during the loop.

This is the main loop of the function. It iterates over each character c in the input string s, and for each character it calculates its corresponding integer value using the romanValues map. It then compares this value to the previous value encountered (prevValue), and if the current value is greater than the previous value, it subtracts twice the previous value from the current value (e.g. for the Roman numeral "IV", prevValue would be 1 and currentValue would be 5, so the result would be 5 - 2 * 1 = 3. If the current value is not greater than the previous value, it simply adds the current value to the result. Finally, it updates prevValue to be equal to currentValue.

This line returns the final integer value of the Roman numeral string.