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            "title": "Number of Ways to Form a Target String Given a Dictionary",
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            "content": "<p>You are given a list of strings of the <strong>same length</strong> <code>words</code> and a string <code>target</code>.</p>\n\n<p>Your task is to form <code>target</code> using the given <code>words</code> under the following rules:</p>\n\n<ul>\n\t<li><code>target</code> should be formed from left to right.</li>\n\t<li>To form the <code>i<sup>th</sup></code> character (<strong>0-indexed</strong>) of <code>target</code>, you can choose the <code>k<sup>th</sup></code> character of the <code>j<sup>th</sup></code> string in <code>words</code> if <code>target[i] = words[j][k]</code>.</li>\n\t<li>Once you use the <code>k<sup>th</sup></code> character of the <code>j<sup>th</sup></code> string of <code>words</code>, you <strong>can no longer</strong> use the <code>x<sup>th</sup></code> character of any string in <code>words</code> where <code>x &lt;= k</code>. In other words, all characters to the left of or at index <code>k</code> become unusuable for every string.</li>\n\t<li>Repeat the process until you form the string <code>target</code>.</li>\n</ul>\n\n<p><strong>Notice</strong> that you can use <strong>multiple characters</strong> from the <strong>same string</strong> in <code>words</code> provided the conditions above are met.</p>\n\n<p>Return <em>the number of ways to form <code>target</code> from <code>words</code></em>. Since the answer may be too large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>\n\n<p>&nbsp;</p>\n<p><strong>Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> words = [&quot;acca&quot;,&quot;bbbb&quot;,&quot;caca&quot;], target = &quot;aba&quot;\n<strong>Output:</strong> 6\n<strong>Explanation:</strong> There are 6 ways to form target.\n&quot;aba&quot; -&gt; index 0 (&quot;<u>a</u>cca&quot;), index 1 (&quot;b<u>b</u>bb&quot;), index 3 (&quot;cac<u>a</u>&quot;)\n&quot;aba&quot; -&gt; index 0 (&quot;<u>a</u>cca&quot;), index 2 (&quot;bb<u>b</u>b&quot;), index 3 (&quot;cac<u>a</u>&quot;)\n&quot;aba&quot; -&gt; index 0 (&quot;<u>a</u>cca&quot;), index 1 (&quot;b<u>b</u>bb&quot;), index 3 (&quot;acc<u>a</u>&quot;)\n&quot;aba&quot; -&gt; index 0 (&quot;<u>a</u>cca&quot;), index 2 (&quot;bb<u>b</u>b&quot;), index 3 (&quot;acc<u>a</u>&quot;)\n&quot;aba&quot; -&gt; index 1 (&quot;c<u>a</u>ca&quot;), index 2 (&quot;bb<u>b</u>b&quot;), index 3 (&quot;acc<u>a</u>&quot;)\n&quot;aba&quot; -&gt; index 1 (&quot;c<u>a</u>ca&quot;), index 2 (&quot;bb<u>b</u>b&quot;), index 3 (&quot;cac<u>a</u>&quot;)\n</pre>\n\n<p><strong>Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> words = [&quot;abba&quot;,&quot;baab&quot;], target = &quot;bab&quot;\n<strong>Output:</strong> 4\n<strong>Explanation:</strong> There are 4 ways to form target.\n&quot;bab&quot; -&gt; index 0 (&quot;<u>b</u>aab&quot;), index 1 (&quot;b<u>a</u>ab&quot;), index 2 (&quot;ab<u>b</u>a&quot;)\n&quot;bab&quot; -&gt; index 0 (&quot;<u>b</u>aab&quot;), index 1 (&quot;b<u>a</u>ab&quot;), index 3 (&quot;baa<u>b</u>&quot;)\n&quot;bab&quot; -&gt; index 0 (&quot;<u>b</u>aab&quot;), index 2 (&quot;ba<u>a</u>b&quot;), index 3 (&quot;baa<u>b</u>&quot;)\n&quot;bab&quot; -&gt; index 1 (&quot;a<u>b</u>ba&quot;), index 2 (&quot;ba<u>a</u>b&quot;), index 3 (&quot;baa<u>b</u>&quot;)\n</pre>\n\n<p>&nbsp;</p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 &lt;= words.length &lt;= 1000</code></li>\n\t<li><code>1 &lt;= words[i].length &lt;= 1000</code></li>\n\t<li>All strings in <code>words</code> have the same length.</li>\n\t<li><code>1 &lt;= target.length &lt;= 1000</code></li>\n\t<li><code>words[i]</code> and <code>target</code> contain only lowercase English letters.</li>\n</ul>\n",
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                    "code": "class Solution(object):\n    def numWays(self, words, target):\n        \"\"\"\n        :type words: List[str]\n        :type target: str\n        :rtype: int\n        \"\"\"\n        ",
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                "For each index i, store the frequency of each character in the ith row.",
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