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
use std::collections::HashMap;

impl Solution {
    pub fn word_pattern(pattern: String, s: String) -> bool {
        let cs1: Vec<char> = pattern.chars().collect();
        let cs2: Vec<&str> = s.split_whitespace().collect();
        let n = cs1.len();
        if n != cs2.len() {
            return false;
        }
        let mut map1 = HashMap::new();
        let mut map2 = HashMap::new();
        for i in 0..n {
            let c = cs1[i];
            let s = cs2[i];
            if !map1.contains_key(&c) {
                map1.insert(c, i);
            }
            if !map2.contains_key(&s) {
                map2.insert(s, i);
            }
            if map1.get(&c) != map2.get(&s) {
                return false;
            }
        }
        true
    }
}
