<p>You are given a string <code>s</code> and an array of strings <code>words</code>. All the strings of <code>words</code> are of <strong>the same length</strong>.</p>

<p>A <strong>concatenated string</strong> is a string that exactly contains all the strings of any permutation of <code>words</code> concatenated.</p>

<ul>
	<li>For example, if <code>words = [&quot;ab&quot;,&quot;cd&quot;,&quot;ef&quot;]</code>, then <code>&quot;abcdef&quot;</code>, <code>&quot;abefcd&quot;</code>, <code>&quot;cdabef&quot;</code>, <code>&quot;cdefab&quot;</code>, <code>&quot;efabcd&quot;</code>, and <code>&quot;efcdab&quot;</code> are all concatenated strings. <code>&quot;acdbef&quot;</code> is not a concatenated string because it is not the concatenation of any permutation of <code>words</code>.</li>
</ul>

<p>Return an array of <em>the starting indices</em> of all the concatenated substrings in <code>s</code>. You can return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;barfoothefoobarman&quot;, words = [&quot;foo&quot;,&quot;bar&quot;]</span></p>

<p><strong>Output:</strong> <span class="example-io">[0,9]</span></p>

<p><strong>Explanation:</strong></p>

<p>The substring starting at 0 is <code>&quot;barfoo&quot;</code>. It is the concatenation of <code>[&quot;bar&quot;,&quot;foo&quot;]</code> which is a permutation of <code>words</code>.<br />
The substring starting at 9 is <code>&quot;foobar&quot;</code>. It is the concatenation of <code>[&quot;foo&quot;,&quot;bar&quot;]</code> which is a permutation of <code>words</code>.</p>
</div>

<p><strong class="example">Example 2:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;wordgoodgoodgoodbestword&quot;, words = [&quot;word&quot;,&quot;good&quot;,&quot;best&quot;,&quot;word&quot;]</span></p>

<p><strong>Output:</strong> <span class="example-io">[]</span></p>

<p><strong>Explanation:</strong></p>

<p>There is no concatenated substring.</p>
</div>

<p><strong class="example">Example 3:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;barfoofoobarthefoobarman&quot;, words = [&quot;bar&quot;,&quot;foo&quot;,&quot;the&quot;]</span></p>

<p><strong>Output:</strong> <span class="example-io">[6,9,12]</span></p>

<p><strong>Explanation:</strong></p>

<p>The substring starting at 6 is <code>&quot;foobarthe&quot;</code>. It is the concatenation of <code>[&quot;foo&quot;,&quot;bar&quot;,&quot;the&quot;]</code>.<br />
The substring starting at 9 is <code>&quot;barthefoo&quot;</code>. It is the concatenation of <code>[&quot;bar&quot;,&quot;the&quot;,&quot;foo&quot;]</code>.<br />
The substring starting at 12 is <code>&quot;thefoobar&quot;</code>. It is the concatenation of <code>[&quot;the&quot;,&quot;foo&quot;,&quot;bar&quot;]</code>.</p>
</div>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= words.length &lt;= 5000</code></li>
	<li><code>1 &lt;= words[i].length &lt;= 30</code></li>
	<li><code>s</code> and <code>words[i]</code> consist of lowercase English letters.</li>
</ul>

class Solution {
public:
    int total_char = 0;
    int word_len = 0;
    unordered_map <string, int> umap;

    void index_words(vector<string> & words){
        for (int i = 0, w = words.size(); i < w; ++i) {
            if (umap.find(words[i]) == umap.end())
               umap[words[i]] = 0;
            umap[words[i]]++;
        }
    }

    // int check_position(const string &s, unordered_map <string, int> &umap, int start_idx, int total_char){
    //     if (total_char == 0) return 1;
    //     if (total_char > s.size() - start_idx) return 0;
    //     if  ((word_len > total_char) || (word_len > s.size() - start_idx)) return 0;
        
    //     string trial_word = "";
    //     for (int j = start_idx; j < start_idx + word_len; ++j)
    //         trial_word.push_back(s[j]);

    //     if (umap.find(trial_word) == umap.end() || umap[trial_word] == 0)
    //         return 0;

    //     //if trial_word matches
    //     int trial_position = start_idx +  word_len;
    //     total_char -= word_len;
    //     umap[trial_word]--;
        
    //     // try the next words
    //     int trial_res = check_position(s, umap, trial_position, total_char);
        
    //     umap[trial_word]++;
    //     total_char += word_len;
        
    //     return trial_res;
    // }

    int check_position(const string &s, unordered_map <string, int> umap, int start_idx){
        int i = start_idx;
        int is_valid = 1;

        // vector<string> used_words(0);
        string trial_word(word_len, ' ');
        while (i < start_idx + total_char) {
            for (int j = i; j < i + word_len; ++j)
                trial_word[j-i] = s[j];   

            unordered_map <string, int>::iterator it = umap.find(trial_word);
            if (it == umap.end() || it->second == 0){
                is_valid = 0;
                break;
            }

            (it->second)--;
            // used_words.push_back(trial_word);
            i += word_len;
        }
        // for (int j = 0, sz = used_words.size(); j < sz; ++j)
        //     umap[used_words[j]]++;
        return is_valid;
    }

    vector<int> findSubstring(string s, vector<string>& words) {
        // counting the total number of characters (total_char)
        int w = words.size();
        if (w > 0)
            word_len = words[0].size();
        total_char = word_len * w;

        // cout << s.size() << " " << words.size() <<endl;
        
        // counting on words
        index_words(words);

        vector<int> res(0);
        for (int i = 0, n = s.size(); i <= n-total_char; ++i)
                if (check_position(s, umap, i))
                    res.push_back(i);
        return res;
    }
};


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