LeetCode 30 - Substring with Concatenation of All Words

Substring with Concatenation of All Words

You are given a string, s, and a list of words, words, that are all of the same length. Find all starting indices of substring(s) in s that is a concatenation of each word in words exactly once and without any intervening characters.

For example, given:
s: "barfoothefoobarman"
words: ["foo", "bar"]

You should return the indices: [0,9].
(order does not matter).

My Code

class Solution {
public:
    vector<int> findSubstring(string s, vector<string>& words) {
        int words_size = words.size();
        int word_len = words[0].length();
        int s_len = s.length();
        unordered_map<string, int> words_cnt;
        for (int i = 0; i < words_size; i++)
            words_cnt[words[i]]++;

        vector<int> indices;
        for (int i = 0; i <= s_len - words_size * word_len; i++)
        {
            unordered_map<string, int> occurences;
            bool flag = true;
            for (int j = 0; j < words_size; j++)
            {
                string word = s.substr(i + j * word_len, word_len);
                if (words_cnt.find(word) != words_cnt.end())
                    occurences[word]++;
                else
                {
                    flag = false;
                    break;
                }

                if (occurences[word] > words_cnt[word])
                {
                    flag = false;
                    break;
                }
            }

            if (flag)
                indices.push_back(i);
        }

        return indices;
    }
};

Runtime: 776 ms

Notice

There may be duplicate word in words. So we need one more unordered_map to record count of each word.