<p>Given two strings <code>s</code> and <code>t</code>, find the number of ways you can choose a non-empty substring of <code>s</code> and replace a <strong>single character</strong> by a different character such that the resulting substring is a substring of <code>t</code>. In other words, find the number of substrings in <code>s</code> that differ from some substring in <code>t</code> by <strong>exactly</strong> one character.</p>

<p>For example, the underlined substrings in <code>&quot;<u>compute</u>r&quot;</code> and <code>&quot;<u>computa</u>tion&quot;</code> only differ by the <code>&#39;e&#39;</code>/<code>&#39;a&#39;</code>, so this is a valid way.</p>

<p>Return <em>the number of substrings that satisfy the condition above.</em></p>

<p>A <strong>substring</strong> is a contiguous sequence of characters within a string.</p>

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

<pre>
<strong>Input:</strong> s = &quot;aba&quot;, t = &quot;baba&quot;
<strong>Output:</strong> 6
<strong>Explanation:</strong> The following are the pairs of substrings from s and t that differ by exactly 1 character:
(&quot;<u>a</u>ba&quot;, &quot;<u>b</u>aba&quot;)
(&quot;<u>a</u>ba&quot;, &quot;ba<u>b</u>a&quot;)
(&quot;ab<u>a</u>&quot;, &quot;<u>b</u>aba&quot;)
(&quot;ab<u>a</u>&quot;, &quot;ba<u>b</u>a&quot;)
(&quot;a<u>b</u>a&quot;, &quot;b<u>a</u>ba&quot;)
(&quot;a<u>b</u>a&quot;, &quot;bab<u>a</u>&quot;)
The underlined portions are the substrings that are chosen from s and t.
</pre>
​​<strong class="example">Example 2:</strong>

<pre>
<strong>Input:</strong> s = &quot;ab&quot;, t = &quot;bb&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong> The following are the pairs of substrings from s and t that differ by 1 character:
(&quot;<u>a</u>b&quot;, &quot;<u>b</u>b&quot;)
(&quot;<u>a</u>b&quot;, &quot;b<u>b</u>&quot;)
(&quot;<u>ab</u>&quot;, &quot;<u>bb</u>&quot;)
​​​​The underlined portions are the substrings that are chosen from s and t.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length, t.length &lt;= 100</code></li>
	<li><code>s</code> and <code>t</code> consist of lowercase English letters only.</li>
</ul>

class Solution {
    struct Node{
        std::unordered_map<char, Node*> children;
        int count{};
        bool isWord{false};
    };

    Node* root{};

    void insert(const std::string& s) {
        Node* node = root;
        for (char c : s) {
            if (!node->children.contains(c)) {
                node->children[c] = new Node{};
            }
            node = node->children[c];
        }

        node->isWord = true;
        ++node->count;

        // std::cout << "inserted string: " << s << " count = " <<  node->count << std::endl;
    }

    int getCount(const std::string& s) {
        Node* node = root;
        for (char c : s) {
            if (!node->children.contains(c)) return 0;
            node = node->children[c];
        }

        return node->count;
    }
public:
    int countSubstrings(string s, string t) {
        root = new Node{};
        int n = s.size(), m = t.size();
        std::vector<bool> chars(26, false);
        for (char c : t) chars[c - 'a'] = true;
        for (int i{}; i < m; ++i) {
            for (int j{i}; j < m; ++j) {
                std::string ss{t.begin() + i, t.begin() + j + 1};
                insert(ss);
            }
        }

        int res{};
        for (int i{}; i < n; ++i) {
            for (int j{i}; j < n; ++j) {
                std::string ss{s.begin() + i, s.begin() + j + 1};
                // std::cout << "Considering: " << ss << std::endl;
                for (char& c : ss) {
                    int orig{c};
                    for (int i{}; i < 26; ++i) {
                        if (chars[i] && (i != (orig - 'a'))) {
                            c = char(i + 'a');
                            // std::cout << "\tFind string: " << ss << std::endl;
                            res += getCount(ss);
                        }
                    }
                    c = orig;
                }
            }
        }

        return res;
    }
};
22000