https://i.imgur.com/kyBhy6o.jpeg
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567. Permutation in String
## 思路
用sliding window 掃s2
檢查固定長度內的char數量是否跟s1相同
## Code
```python
class Solution:
def checkInclusion(self, s1: str, s2: str) -> bool:
if len(s1) > len(s2):
return False
n = len(s1)
target = Counter(s1)
count = Counter()
for idx, ch in enumerate(s2):
count[ch] += 1
if idx >= n:
count[s2[idx-n]] -= 1
if count == target:
return True
return False
```
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