find-all-anagrams-in-a-string

Find All Anagrams in a String

LeetCode #: 438

Difficulty: Medium.

Topics: Hash Table.

Problems

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 Explanation

This solution uses sliding window technique.

Reference: LeetCode Discuss - Shortest/Concise JAVA O(n) Sliding Window Solution

Complexity Analysis

Time complexity: O(p+s). We iterate through each character in p and s once.

Space complexity: O(1). We use an array with fixed length of 26 to keep track of character count.