LeetCode 438. Find All Anagrams in a String

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题目

Given a string s and a non-empty string p, find all the start indices of p‘s anagrams in s.

Strings consists of lowercase English letters only and the length of both strings s and p will not be larger than 20,100.

The order of output does not matter.

Example 1:

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Input:
s: "cbaebabacd" p: "abc"

Output:
[0, 6]

Explanation:
The substring with start index = 0 is "cba", which is an anagram of "abc".
The substring with start index = 6 is "bac", which is an anagram of "abc".

Example 2:

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Input:
s: "abab" p: "ab"

Output:
[0, 1, 2]

Explanation:
The substring with start index = 0 is "ab", which is an anagram of "ab".
The substring with start index = 1 is "ba", which is an anagram of "ab".
The substring with start index = 2 is "ab", which is an anagram of "ab".

思路

滑动窗口+双指针。

代码

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class Solution(object):
    def findAnagrams(self, s, p):
        """
        :type s: str
        :type p: str
        :rtype: List[int]
        """
        res = []
        counter = collections.Counter()
        pcounter = collections.Counter(p)
        l, r = 0, 0
        while r < len(s):
            counter[s[r]] += 1
            if r-l+1 == len(p):
                if pcounter == counter:
                    res.append(l)
                counter[s[l]] -= 1
                if counter[s[l]] == 0:
                    del counter[s[l]]
                l += 1
            r += 1
        return res