809. Expressive Words

Sometimes people repeat letters to represent extra feeling. For example:

• “hello” -> “heeellooo”
• “hi” -> “hiiii”

In these strings like “heeellooo”, we have groups of adjacent letters that are all the same: “h”, “eee”, “ll”, “ooo”.

You are given a string s and an array of query strings words. A query word is stretchy if it can be made to be equal to s by any number of applications of the following extension operation: choose a group consisting of characters c, and add some number of characters c to the group so that the size of the group is three or more.

• For example, starting with “hello”, we could do an extension on the group “o” to get “hellooo”, but we cannot get “helloo” since the group “oo” has a size less than three. Also, we could do another extension like “ll” -> “lllll” to get “helllllooo”. If s = “helllllooo”, then the query word “hello” would be stretchy because of these two extension operations: query = “hello” -> “hellooo” -> “helllllooo” = s.

Return the number of query strings that are stretchy.

class Solution {
    bool equal(char a, char b, char c) {
        return a == b && b == c;
    }
    bool compare(string& s, string &w) {
        int j(0), slen(s.length()), wlen(w.length());
        for(int i(0);i < slen; i++) {
            if(s[i] == w[j] and j < wlen) j++;
            else if(0 < i and i < slen - 1 and equal(s[i - 1], s[i], s[i + 1]));
            else if(i > 1 and equal(s[i - 2], s[i - 1], s[i]));
            else return false;
        }
        return j == wlen;
    }
public:
    int expressiveWords(string s, vector<string>& words) {
        int res(0);
        for(auto& w : words) {
            if(compare(s, w)) ++res;
        }
        return res;
    }
};