# Problem 438: Find All Anagrams in a String

> <https://leetcode.com/problems/find-all-anagrams-in-a-string/>

## 思路

* 这道题的思路还是 sliding window 的经典思路：首先用一个 map 把 target 字符串的元素都存进去，接下来就慢慢地滑动窗口，遇到 map 中有的元素就 count--，当 count 为 0 的时候，说明我们的窗口中已经填满了这个元素
* 当窗口的 size 已经大于一个 target 字符串的时候，我们开始移动 left&#x20;

```java
public class Solution {
    public List<Integer> findAnagrams(String s, String p) {
        List<Integer> rst = new ArrayList<Integer>();
        if (s == null || p == null || s.length() == 0 || p.length() == 0) {
            return rst;
        }

        int[] map = new int[128];
        for (char c : p.toCharArray()) {
            map[c]++;
        }
        int left = 0, right = 0, count = p.length();
        while (right < s.length()) {
            if (map[s.charAt(right)] > 0) {
                count--;
            }
            map[s.charAt(right)]--;
            right++;

            if (count == 0) {
                rst.add(left);
            }

            if (right - left == p.length()) {
                if (map[s.charAt(left)] >= 0) {
                    count++;
                }
                map[s.charAt(left)]++;
                left++;
            }
        }

        return rst;
    }
}
```

## 易错点

1. 条件判断

   ```java
   if (right - left == p.length()) {
        if (map[s.charAt(left)] >= 0) {
            count++;
        }
        map[s.charAt(left)]++;
        left++;
   }
   ```

   其中 `map[s.charAt(left)] >= 0`意味着，原先这个 char 就是在 p 中的，否则经过不断地 --，已经小于 0 了。


---

# 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://liuyang89116.gitbook.io/my-leetcode-book/chapter_2_string/sliding-window-problems/problem-438-find-all-anagrams-in-a-string.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.