3019. Number of Changing Keys

You are given a 0-indexed string s typed by a user. Changing a key is defined as using a key different from the last used key. For example, s = "ab" has a change of a key while s = "bBBb" does not have any.

Return the number of times the user had to change the key.

Note: Modifiers like shift or caps lock won’t be counted in changing the key that is if a user typed the letter 'a' and then the letter 'A' then it will not be considered as a changing of key.

class Solution {
public:
    int countKeyChanges(string s) {
        int res = 0;
        for(int i = 0; i < s.length() - 1; i++) {
            char a = s[i], b = s[i+1];
            if(isupper(a)) a = tolower(a);
            if(isupper(b)) b = ::tolower(b);
            if(a != b) res += 1;
        } 
        return res;
    }
};