LeetCode: Permutation in String Solution

Notice the constraints

Approach

Notice that there's a constraint "s1 and s2 consist of lowercase English letters"

Maintain a sliding window with size of s1.length

Use a counter base on character occurences to detect for permutation

Question now turns to "check if two strings are permutation of each other"

Implementation

1var checkInclusion = function (s1, s2) {
2 let [n1, n2] = [s1.length, s2.length]
3 let occurences = Array(26).fill(0)
4
5 const mutate = (charCode, dir) =>
6 (occurences[charCode - "a".charCodeAt(0)] += dir)
7
8 const isMatch = () => occurences.every(x => x === 0)
9
10 for (let i = 0; i < n1; i++) {
11 mutate(s1.charCodeAt(i), +1)
12 }
13
14 for (let i = 0; i < n2; i++) {
15 mutate(s2.charCodeAt(i), -1)
16 if (i - n1 >= 0) mutate(s2.charCodeAt(i - n1), +1)
17
18 if (isMatch()) return true
19 }
20
21 return false
22}

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Tags

leetcode

string

hash table

sliding window

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