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77 lines
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77 lines
3.0 KiB
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<p>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>，求该后缀表达式的计算结果。</p>
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<p>有效的算符包括 <code>+</code>、<code>-</code>、<code>*</code>、<code>/</code> 。每个运算对象可以是整数，也可以是另一个逆波兰表达式。</p>
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<p> </p>
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<p><strong>说明：</strong></p>
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<ul>
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<li>整数除法只保留整数部分。</li>
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<li>给定逆波兰表达式总是有效的。换句话说，表达式总会得出有效数值且不存在除数为 0 的情况。</li>
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</ul>
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<p> </p>
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<p><strong>示例 1：</strong></p>
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<pre>
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<strong>输入：</strong>tokens = ["2","1","+","3","*"]
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<strong>输出：</strong>9
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<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
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</pre>
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<p><strong>示例 2：</strong></p>
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<pre>
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<strong>输入：</strong>tokens = ["4","13","5","/","+"]
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<strong>输出：</strong>6
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<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
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</pre>
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<p><strong>示例 3：</strong></p>
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<pre>
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<strong>输入：</strong>tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
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<strong>输出：</strong>22
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<strong>解释：</strong>
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该算式转化为常见的中缀算术表达式为：
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((10 * (6 / ((9 + 3) * -11))) + 17) + 5
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= ((10 * (6 / (12 * -11))) + 17) + 5
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= ((10 * (6 / -132)) + 17) + 5
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= ((10 * 0) + 17) + 5
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= (0 + 17) + 5
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= 17 + 5
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= 22</pre>
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<p> </p>
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<p><strong>提示：</strong></p>
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<ul>
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<li><code>1 <= tokens.length <= 10<sup>4</sup></code></li>
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<li><code>tokens[i]</code> 要么是一个算符（<code>"+"</code>、<code>"-"</code>、<code>"*"</code> 或 <code>"/"</code>），要么是一个在范围 <code>[-200, 200]</code> 内的整数</li>
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</ul>
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<p> </p>
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<p><strong>逆波兰表达式：</strong></p>
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<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>
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<ul>
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<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>
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<li>该算式的逆波兰表达式写法为 <code>( ( 1 2 + ) ( 3 4 + ) * )</code> 。</li>
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</ul>
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<p>逆波兰表达式主要有以下两个优点：</p>
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<ul>
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<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>
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<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>
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</ul>
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<p> </p>
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<p><meta charset="UTF-8" />注意：本题与主站 150 题相同： <a href="https://leetcode-cn.com/problems/evaluate-reverse-polish-notation/">https://leetcode-cn.com/problems/evaluate-reverse-polish-notation/</a></p>
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