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Description
tab: English
<p>You have intercepted a secret message encoded as a string of numbers. The message is <strong>decoded</strong> via the following mapping:</p>
<p><code>"1" -> 'A'<br />
"2" -> 'B'<br />
...<br />
"25" -> 'Y'<br />
"26" -> 'Z'</code></p>
<p>However, while decoding the message, you realize that there are many different ways you can decode the message because some codes are contained in other codes (<code>"2"</code> and <code>"5"</code> vs <code>"25"</code>).</p>
<p>For example, <code>"11106"</code> can be decoded into:</p>
<ul>
<li><code>"AAJF"</code> with the grouping <code>(1, 1, 10, 6)</code></li>
<li><code>"KJF"</code> with the grouping <code>(11, 10, 6)</code></li>
<li>The grouping <code>(1, 11, 06)</code> is invalid because <code>"06"</code> is not a valid code (only <code>"6"</code> is valid).</li>
</ul>
<p>Note: there may be strings that are impossible to decode.<br />
<br />
Given a string s containing only digits, return the <strong>number of ways</strong> to <strong>decode</strong> it. If the entire string cannot be decoded in any valid way, return <code>0</code>.</p>
<p>The test cases are generated so that the answer fits in a <strong>32-bit</strong> integer.</p>
<p> </p>
<p><strong class="example">Example 1:</strong></p>
<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = "12"</span></p>
<p><strong>Output:</strong> <span class="example-io">2</span></p>
<p><strong>Explanation:</strong></p>
<p>"12" could be decoded as "AB" (1 2) or "L" (12).</p>
</div>
<p><strong class="example">Example 2:</strong></p>
<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = "226"</span></p>
<p><strong>Output:</strong> <span class="example-io">3</span></p>
<p><strong>Explanation:</strong></p>
<p>"226" could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).</p>
</div>
<p><strong class="example">Example 3:</strong></p>
<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = "06"</span></p>
<p><strong>Output:</strong> <span class="example-io">0</span></p>
<p><strong>Explanation:</strong></p>
<p>"06" cannot be mapped to "F" because of the leading zero ("6" is different from "06"). In this case, the string is not a valid encoding, so return 0.</p>
</div>
<p> </p>
<p><strong>Constraints:</strong></p>
<ul>
<li><code>1 <= s.length <= 100</code></li>
<li><code>s</code> contains only digits and may contain leading zero(s).</li>
</ul>
---
[submissions](https://leetcode.com/problems/decode-ways/submissions/) | [solutions](https://leetcode.com/problems/decode-ways/solutions/)
tab: 中文
<p>一条包含字母 <code>A-Z</code> 的消息通过以下映射进行了 <strong>编码</strong> ：</p>
<p><code>"1" -> 'A'<br />
"2" -> 'B'<br />
...<br />
"25" -> 'Y'<br />
"26" -> 'Z'</code></p>
<p>然而，在 <strong>解码</strong> 已编码的消息时，你意识到有许多不同的方式来解码，因为有些编码被包含在其它编码当中（<code>"2"</code> 和 <code>"5"</code> 与 <code>"25"</code>）。</p>
<p>例如，<code>"11106"</code> 可以映射为：</p>
<ul>
<li><code>"AAJF"</code> ，将消息分组为 <code>(1, 1, 10, 6)</code></li>
<li><code>"KJF"</code> ，将消息分组为 <code>(11, 10, 6)</code></li>
<li>消息不能分组为 <code>(1, 11, 06)</code> ，因为 <code>"06"</code> 不是一个合法编码（只有 "6" 是合法的）。</li>
</ul>
<p>注意，可能存在无法解码的字符串。</p>
<p>给你一个只含数字的 <strong>非空 </strong>字符串 <code>s</code> ，请计算并返回 <strong>解码</strong> 方法的 <strong>总数</strong> 。如果没有合法的方式解码整个字符串，返回 <code>0</code>。</p>
<p>题目数据保证答案肯定是一个 <strong>32 位</strong> 的整数。</p>
<p> </p>
<p><strong>示例 1：</strong></p>
<pre>
<strong>输入：</strong>s = "12"
<strong>输出：</strong>2
<strong>解释：</strong>它可以解码为 "AB"（1 2）或者 "L"（12）。
</pre>
<p><strong>示例 2：</strong></p>
<pre>
<strong>输入：</strong>s = "226"
<strong>输出：</strong>3
<strong>解释：</strong>它可以解码为 "BZ" (2 26), "VF" (22 6), 或者 "BBF" (2 2 6) 。
</pre>
<p><strong>示例 3：</strong></p>
<pre>
<strong>输入：</strong>s = "06"
<strong>输出：</strong>0
<strong>解释：</strong>"06" 无法映射到 "F" ，因为存在前导零（"6" 和 "06" 并不等价）。
</pre>
<p> </p>
<p><strong>提示：</strong></p>
<ul>
<li><code>1 <= s.length <= 100</code></li>
<li><code>s</code> 只包含数字，并且可能包含前导零。</li>
</ul>
---
[提交记录](https://leetcode.cn/problems/decode-ways/submissions/) | [题解](https://leetcode.cn/problems/decode-ways/solution/)
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