Problem

题目大意：在s中找出所有p的Anagrams。

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

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:

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:

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".

Solution: HashTable + Sliding Window

Time complexity: O(n)

Space complexity: O(n)

C++

// Author: Huahua
// Running time: 35 ms
class Solution {
public:
  vector<int> findAnagrams(string s, string p) {
    int n = s.length();
    int l = p.length();
    vector<int> ans;
    vector<int> vp(26, 0);
    vector<int> vs(26, 0);
    for (char c : p) ++vp[c - 'a'];    
    for (int i = 0; i < n; ++i) {
      if (i >= l) --vs[s[i - l] - 'a'];        
      ++vs[s[i] - 'a'];
      if (vs == vp) ans.push_back(i + 1 - l);
    }
    return ans;
  }
};

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