<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 {
    bool check(string s, map<string, int>& freq, int word_len,
    int num_words) {
        int l = s.length();
        unordered_map<string,int> temp_freq;
        int same_freq_words = 0;
        for (int i = 0; i < l - word_len + 1; i += word_len) {
            string window = s.substr(i, word_len);
            temp_freq[window]+=1;
            if (temp_freq[window] == freq[window]) 
                same_freq_words+=1;
        }
        return (same_freq_words == num_words);
    }

public:
    vector<int> findSubstring(string s, vector<string>& words) {
        int len = s.length();
        int word_len = words[0].length();
        int num_words = words.size();
        int window_len = word_len * num_words;
        int curr_same_freq = 0;
        int diff_characters = 0;
        vector<int> char_freq(26, 0);
        map<string, int> freq;
        vector<int> ans;
        vector<int> curr_char_freq(26, 0);
        map<string,bool> valid;

        for (string x : words) {
            freq[x]++;
            for (char y : x) {
                char_freq[y - 'a']++;
                if (char_freq[y - 'a'] == 1) diff_characters += 1;
            }
        }
        int dist_words = freq.size();
        int left = 0;
        int right = 0;

        while (right < len) {
            int char_index = s[right] - 'a';
            curr_char_freq[char_index]++;

            if (curr_char_freq[char_index] == char_freq[char_index]) curr_same_freq++;
            if (right - left + 1 == window_len) {
                if (curr_same_freq == diff_characters) {
                    string window = s.substr(left, window_len);
                    if(valid.find(window) != valid.end() && valid[window] == true) ans.push_back(left);
                    else {
                        bool is_valid = check(window, freq, word_len,dist_words);
                        if (is_valid) {
                            valid[window] = true;
                            ans.push_back(left);
                        }
                        else valid[window] = false;
                    }
                }
                char_index = s[left] - 'a';
                if (curr_char_freq[char_index] == char_freq[char_index]) curr_same_freq--;
                curr_char_freq[char_index]--;
                left++;
            }
            right++;
        }

        return ans;
    }
};

103962