LeetCode Reverse Words in a String

class Solution {
public:
    void reverseWords(string &s) {
        int len = s.length();
        reverse(s.begin(), s.end());
        int wpos = 0;
        for (int p=0, q=0; p < len; p = q) {
            while ((p<len) && (s[p] == ‘ ‘)) p++;
            q = p;
            while ((q<len) && (s[q] != ‘ ‘)) q++;
            reverse(s.begin() + p, s.begin() + q);
            if (wpos != 0 && p < q) s[wpos++] = ‘ ‘;
            for (int i=p; i<q; i++) {
                s[wpos++] = s[i];
            }
        }
        if (wpos != len) s = s.substr(0, wpos);
    }
};