3561. Resulting String After Adjacent Removals

You are given a string s consisting of lowercase English letters.

You must repeatedly perform the following operation while the string s has at least two consecutive characters:

• Remove the leftmost pair of adjacent characters in the string that are consecutive in the alphabet, in either order (e.g., 'a' and 'b', or 'b' and 'a').
• Shift the remaining characters to the left to fill the gap.

Return the resulting string after no more operations can be performed.

Note: Consider the alphabet as circular, thus 'a' and 'z' are consecutive.

class Solution {
    bool cons(char a, char b) {
        int d = abs(a-b);
        return d == 1 or d == 25;
    }
public:
    string resultingString(string s) {
        string res = "";
        for(auto& ch : s) {
            if(res.length() and cons(res.back(), ch)) res.pop_back();
            else res.push_back(ch);
        }
        return res;
    }
};