<p>Given two strings <code>word1</code> and <code>word2</code>, return <em>the minimum number of operations required to convert <code>word1</code> to <code>word2</code></em>.</p>

<p>You have the following three operations permitted on a word:</p>

<ul>
	<li>Insert a character</li>
	<li>Delete a character</li>
	<li>Replace a character</li>
</ul>

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

<pre>
<strong>Input:</strong> word1 = &quot;horse&quot;, word2 = &quot;ros&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong> 
horse -&gt; rorse (replace &#39;h&#39; with &#39;r&#39;)
rorse -&gt; rose (remove &#39;r&#39;)
rose -&gt; ros (remove &#39;e&#39;)
</pre>

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

<pre>
<strong>Input:</strong> word1 = &quot;intention&quot;, word2 = &quot;execution&quot;
<strong>Output:</strong> 5
<strong>Explanation:</strong> 
intention -&gt; inention (remove &#39;t&#39;)
inention -&gt; enention (replace &#39;i&#39; with &#39;e&#39;)
enention -&gt; exention (replace &#39;n&#39; with &#39;x&#39;)
exention -&gt; exection (replace &#39;n&#39; with &#39;c&#39;)
exection -&gt; execution (insert &#39;u&#39;)
</pre>

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

<ul>
	<li><code>0 &lt;= word1.length, word2.length &lt;= 500</code></li>
	<li><code>word1</code> and <code>word2</code> consist of lowercase English letters.</li>
</ul>

class Solution {
public:

    int solve(string s, string t, vector<vector<int>>&v){
        if(s==""){
            return t.length();
        }
        if(t==""){
            return s.length();
        }
        int m=s.length();
        int n=t.length();
        if(v[m][n]!=-1)
        return v[m][n];
        int count=0;
        if(s[m-1]==t[n-1]){
            count = solve(s.substr(0,m-1), t.substr(0,n-1), v);
        }
        else{
            count = 1 + min(solve(s.substr(0,m), t.substr(0,n-1), v), min(solve(s.substr(0,m-1), t.substr(0,n), v), solve(s.substr(0,m-1), t.substr(0,n-1), v)));
        }
        v[m][n] = count;
        return count;
    }
    int minDistance(string s, string t) {
        int m=s.length();
        int n=t.length();
        vector<vector<int>>v(m+1, vector<int>(n+1,-1));
        int count = solve(s, t, v);
        return count;
    }
};
51201