# 逆波兰表达式求值

题目链接: <https://leetcode.cn/problems/evaluate-reverse-polish-notation>

## 解题思路：

1. 遍历tokens，判断是否是算符，是则从栈顶出栈两个元素进行计算
2. 否则，转换成int，入栈

```go
func evalRPN(tokens []string) int {
	queue := make([]int, 0)
	for _, item := range tokens {
		last := len(queue) - 1
		switch item {
		case "+":
			val1, val2 := queue[last], queue[last-1]
			queue = append(queue[:last-1], val2+val1)
		case "-":
			val1, val2 := queue[last], queue[last-1]
			queue = append(queue[:last-1], val2-val1)
		case "*":
			val1, val2 := queue[last], queue[last-1]
			queue = append(queue[:last-1], val2*val1)
		case "/":
			val1, val2 := queue[last], queue[last-1]
			queue = append(queue[:last-1], val2/val1)
		default:
			data, _ := strconv.Atoi(item)
			queue = append(queue, data)
		}
	}
	return queue[0]
}
```

## 复杂度分析

* **时间复杂度：** 只遍历了一遍tokens，因此时间复杂度为 $$O(n)$$，其中 $$n$$ 是字符串数组 `tokens` 的长度
* **空间复杂度：** 只使用了一个栈，因此空间复杂度为 $$O(n)$$，


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://leetcodebook-1.gitbook.io/top-interview-150/stack/evaluate-reverse-polish-notation.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.