Word Pattern
<p>Given a <code>pattern</code> and a string <code>s</code>, find if <code>s</code>&nbsp;follows the same pattern.</p>

<p>Here <b>follow</b> means a full match, such that there is a bijection between a letter in <code>pattern</code> and a <b>non-empty</b> word in <code>s</code>. Specifically:</p>

<ul>
	<li>Each letter in <code>pattern</code> maps to <strong>exactly</strong> one unique word in <code>s</code>.</li>
	<li>Each unique word in <code>s</code> maps to <strong>exactly</strong> one letter in <code>pattern</code>.</li>
	<li>No two letters map to the same word, and no two words map to the same letter.</li>
</ul>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">pattern = &quot;abba&quot;, s = &quot;dog cat cat dog&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">true</span></p>

<p><strong>Explanation:</strong></p>

<p>The bijection can be established as:</p>

<ul>
	<li><code>&#39;a&#39;</code> maps to <code>&quot;dog&quot;</code>.</li>
	<li><code>&#39;b&#39;</code> maps to <code>&quot;cat&quot;</code>.</li>
</ul>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">pattern = &quot;abba&quot;, s = &quot;dog cat cat fish&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">false</span></p>
</div>

<p><strong class="example">Example 3:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">pattern = &quot;aaaa&quot;, s = &quot;dog cat cat dog&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">false</span></p>
</div>

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

<ul>
	<li><code>1 &lt;= pattern.length &lt;= 300</code></li>
	<li><code>pattern</code> contains only lower-case English letters.</li>
	<li><code>1 &lt;= s.length &lt;= 3000</code></li>
	<li><code>s</code> contains only lowercase English letters and spaces <code>&#39; &#39;</code>.</li>
	<li><code>s</code> <strong>does not contain</strong> any leading or trailing spaces.</li>
	<li>All the words in <code>s</code> are separated by a <strong>single space</strong>.</li>
</ul>
Hash Table; String
public class Solution {
    public bool WordPattern(string pattern, string s) {
        var ws = s.Split(' ');
        if (pattern.Length != ws.Length) {
            return false;
        }
        var d1 = new Dictionary<char, string>();
        var d2 = new Dictionary<string, char>();
        for (int i = 0; i < ws.Length; ++i) {
            var a = pattern[i];
            var b = ws[i];
            if (d1.ContainsKey(a) && d1[a] != b) {
                return false;
            }
            if (d2.ContainsKey(b) && d2[b] != a) {
                return false;
            }
            d1[a] = b;
            d2[b] = a;
        }
        return true;
    }
}
