Nav: << previous: 149.直线上最多的点数 | next: 151.反转字符串中的单词 >>
Description
tab: English
<p>You are given an array of strings <code>tokens</code> that represents an arithmetic expression in a <a href="http://en.wikipedia.org/wiki/Reverse_Polish_notation" target="_blank">Reverse Polish Notation</a>.</p>
<p>Evaluate the expression. Return <em>an integer that represents the value of the expression</em>.</p>
<p><strong>Note</strong> that:</p>
<ul>
<li>The valid operators are <code>'+'</code>, <code>'-'</code>, <code>'*'</code>, and <code>'/'</code>.</li>
<li>Each operand may be an integer or another expression.</li>
<li>The division between two integers always <strong>truncates toward zero</strong>.</li>
<li>There will not be any division by zero.</li>
<li>The input represents a valid arithmetic expression in a reverse polish notation.</li>
<li>The answer and all the intermediate calculations can be represented in a <strong>32-bit</strong> integer.</li>
</ul>
<p> </p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong> tokens = ["2","1","+","3","*"]
<strong>Output:</strong> 9
<strong>Explanation:</strong> ((2 + 1) * 3) = 9
</pre>
<p><strong class="example">Example 2:</strong></p>
<pre>
<strong>Input:</strong> tokens = ["4","13","5","/","+"]
<strong>Output:</strong> 6
<strong>Explanation:</strong> (4 + (13 / 5)) = 6
</pre>
<p><strong class="example">Example 3:</strong></p>
<pre>
<strong>Input:</strong> tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
<strong>Output:</strong> 22
<strong>Explanation:</strong> ((10 * (6 / ((9 + 3) * -11))) + 17) + 5
= ((10 * (6 / (12 * -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22
</pre>
<p> </p>
<p><strong>Constraints:</strong></p>
<ul>
<li><code>1 <= tokens.length <= 10<sup>4</sup></code></li>
<li><code>tokens[i]</code> is either an operator: <code>"+"</code>, <code>"-"</code>, <code>"*"</code>, or <code>"/"</code>, or an integer in the range <code>[-200, 200]</code>.</li>
</ul>
---
[submissions](https://leetcode.com/problems/evaluate-reverse-polish-notation/submissions/) | [solutions](https://leetcode.com/problems/evaluate-reverse-polish-notation/solutions/)
tab: 中文
<p>给你一个字符串数组 <code>tokens</code> ，表示一个根据 <a href="https://baike.baidu.com/item/%E9%80%86%E6%B3%A2%E5%85%B0%E5%BC%8F/128437" target="_blank">逆波兰表示法</a> 表示的算术表达式。</p>
<p>请你计算该表达式。返回一个表示表达式值的整数。</p>
<p><strong>注意：</strong></p>
<ul>
<li>有效的算符为 <code>'+'</code>、<code>'-'</code>、<code>'*'</code> 和 <code>'/'</code> 。</li>
<li>每个操作数（运算对象）都可以是一个整数或者另一个表达式。</li>
<li>两个整数之间的除法总是 <strong>向零截断</strong> 。</li>
<li>表达式中不含除零运算。</li>
<li>输入是一个根据逆波兰表示法表示的算术表达式。</li>
<li>答案及所有中间计算结果可以用 <strong>32 位</strong> 整数表示。</li>
</ul>
<p> </p>
<p><strong>示例 1：</strong></p>
<pre>
<strong>输入：</strong>tokens = ["2","1","+","3","*"]
<strong>输出：</strong>9
<strong>解释：</strong>该算式转化为常见的中缀算术表达式为：((2 + 1) * 3) = 9
</pre>
<p><strong>示例 2：</strong></p>
<pre>
<strong>输入：</strong>tokens = ["4","13","5","/","+"]
<strong>输出：</strong>6
<strong>解释：</strong>该算式转化为常见的中缀算术表达式为：(4 + (13 / 5)) = 6
</pre>
<p><strong>示例 3：</strong></p>
<pre>
<strong>输入：</strong>tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
<strong>输出：</strong>22
<strong>解释：</strong>该算式转化为常见的中缀算术表达式为：
((10 * (6 / ((9 + 3) * -11))) + 17) + 5
= ((10 * (6 / (12 * -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22</pre>
<p> </p>
<p><strong>提示：</strong></p>
<ul>
<li><code>1 <= tokens.length <= 10<sup>4</sup></code></li>
<li><code>tokens[i]</code> 是一个算符（<code>"+"</code>、<code>"-"</code>、<code>"*"</code> 或 <code>"/"</code>），或是在范围 <code>[-200, 200]</code> 内的一个整数</li>
</ul>
<p> </p>
<p><strong>逆波兰表达式：</strong></p>
<p>逆波兰表达式是一种后缀表达式，所谓后缀就是指算符写在后面。</p>
<ul>
<li>平常使用的算式则是一种中缀表达式，如 <code>( 1 + 2 ) * ( 3 + 4 )</code> 。</li>
<li>该算式的逆波兰表达式写法为 <code>( ( 1 2 + ) ( 3 4 + ) * )</code> 。</li>
</ul>
<p>逆波兰表达式主要有以下两个优点：</p>
<ul>
<li>去掉括号后表达式无歧义，上式即便写成 <code>1 2 + 3 4 + * </code>也可以依据次序计算出正确结果。</li>
<li>适合用栈操作运算：遇到数字则入栈；遇到算符则取出栈顶两个数字进行计算，并将结果压入栈中</li>
</ul>
---
[提交记录](https://leetcode.cn/problems/evaluate-reverse-polish-notation/submissions/) | [题解](https://leetcode.cn/problems/evaluate-reverse-polish-notation/solution/)
Solutions & Notes
properties:
note.updated:
displayName: Last Updated
note.relative_links:
displayName: Related Links
note.desc:
displayName: Description
note.grade:
displayName: Rating
note.program_language:
displayName: Language
note.time_complexity:
displayName: TC
note.space_complexity:
displayName: SC
views:
- type: table
name: Solutions & Notes
filters:
and:
- file.hasLink(this.file)
- file.tags.containsAny("leetcode/solution", "leetcode/note")
order:
- file.name
- desc
- program_language
- time_complexity
- space_complexity
- grade
- relative_links
- updated
sort:
- property: grade
direction: ASC
- property: time_complexity
direction: ASC
- property: program_language
direction: ASC
columnSize:
file.name: 104
note.space_complexity: 65
note.grade: 126
Similar Problems
properties:
note.lcTopics:
displayName: Topics
note.lcAcRate:
displayName: AC Rate
note.favorites:
displayName: Favorites
note.grade:
displayName: Rating
note.translatedTitle:
displayName: Title (CN)
note.lcDifficulty:
displayName: Difficulty
views:
- type: table
name: Similar Problems
filters:
and:
- file.hasLink(this.file)
- similarQuestions.contains(this.file)
order:
- file.name
- translatedTitle
- lcTopics
- lcDifficulty
- lcAcRate
- grade
- favorites
sort:
- property: file.name
direction: ASC
- property: lcTopics
direction: DESC
columnSize:
note.translatedTitle: 240
note.lcTopics: 347
note.lcAcRate: 75
note.grade: 122