3216. Lexicographically Smallest String After a Swap

Given a string s containing only digits, return the

lexicographically smallest string

that can be obtained after swapping adjacent digits in s with the same parity at most once.

Digits have the same parity if both are odd or both are even. For example, 5 and 9, as well as 2 and 4, have the same parity, while 6 and 9 do not.

class Solution {
    bool ok(char ch, char ch2) {
        if((ch ^ ch2) % 2 == 1) return false; 
        return ch > ch2;
    }
public:
    string getSmallestString(string s) {
        int n = s.length();
        for(int i = 1; i < n; i++) {
            if(ok(s[i-1], s[i])) {
                swap(s[i], s[i-1]);
                return s;
            }
        }
        return s;
    }
};