<p>Given two strings <code>word1</code> and <code>word2</code>, return <em>the minimum number of <strong>steps</strong> required to make</em> <code>word1</code> <em>and</em> <code>word2</code> <em>the same</em>.</p>

<p>In one <strong>step</strong>, you can delete exactly one character in either string.</p>

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

<pre>
<strong>Input:</strong> word1 = &quot;sea&quot;, word2 = &quot;eat&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> You need one step to make &quot;sea&quot; to &quot;ea&quot; and another step to make &quot;eat&quot; to &quot;ea&quot;.
</pre>

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

<pre>
<strong>Input:</strong> word1 = &quot;leetcode&quot;, word2 = &quot;etco&quot;
<strong>Output:</strong> 4
</pre>

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

<ul>
	<li><code>1 &lt;= word1.length, word2.length &lt;= 500</code></li>
	<li><code>word1</code> and <code>word2</code> consist of only lowercase English letters.</li>
</ul>

struct StringKey {
    string_view s1;
    string_view s2;

    bool operator==(const StringKey& rhs) const = default;
};

template<>
struct std::hash<StringKey> {
    size_t operator()(const StringKey& sk) const {
        return (std::hash<string_view>()(sk.s1) << 1) | std::hash<string_view>()(sk.s2);
    }
};

class Solution {
    unordered_map<StringKey, int> minmap;

    int minDistHelper(string_view s1, string_view s2) {
        if(s1.empty())
            return s2.length();
        if(s2.empty())
            return s1.length();

        StringKey sk = {s1, s2};
        auto it = minmap.find(sk);
        if(it != minmap.end())
            return it->second;

        int mdist = 0;
        if(s1[0] == s2[0]) {
            mdist = minDistHelper(s1.substr(1), s2.substr(1));
        } else {
            int mdist1 = minDistHelper(s1.substr(1), s2);
            int mdist2 = minDistHelper(s1, s2.substr(1));
            mdist = min(mdist1, mdist2) + 1;
        }

        minmap[sk] = mdist;
        return mdist;
    }
public:
    int minDistance(string word1, string word2) {
        return minDistHelper(word1, word2);
    }
};
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