Leetcode 567. Permutation in String

https://leetcode.com/problems/permutation-in-string/description/
https://discuss.leetcode.com/topic/87845/java-solution-sliding-window
感谢@shawngao的sliding-window的提示

Given two strings s1 and s2, write a function to return true if s2 contains the permutation of s1. In other words, one of the first string’s permutations is the substring of the second string.

Example 1:

Input:s1 = "ab" s2 = "eidbaooo"Output:TrueExplanation: s2 contains one permutation of s1 ("ba").

Example 2:

Input:s1= "ab" s2 = "eidboaoo"Output: False

Note:
The input strings only contain lower case letters.
The length of both given strings is in range [1, 10,000].

暴力解法肯定会爆炸。
有了想统计单个char的想法，然后看见discuss中sliding-window的时候，思路一下子就豁然开朗了，通过在s2上维护一个s1长的sliding-window，然后统计这段长度中的char的数量，若与s1的数量一致，则意味着s2的这段子串是s1的一个排列。
结合javascript的语言结构，hash统计的实现很是简单

var checkInclusion = function(s1, s2) {    if (s2.length < s1.length || s2.length == 0) {        return false;    }    const hashMap = {};    const len = s1.length;    for (let i = 0; i < len; ++i) {        if (!hashMap[s1[i]]) {            hashMap[s1[i]] = 0;        }        if (!hashMap[s2[i]]) {            hashMap[s2[i]] = 0;        }        hashMap[s1[i]]++;        hashMap[s2[i]]--;    }    if (isAllZero(hashMap)) {        return true;    }    for (let i = len; i < s2.length; ++i) {        if (!hashMap[s2[i]]) {            hashMap[s2[i]] = 0;        }        hashMap[s2[i]]--;        hashMap[s2[i-len]]++;        if (isAllZero(hashMap)) {            return true;        }    }    return false;};const isAllZero = (hashMap) => {    const keys = Object.keys(hashMap);    for (let i = 0; i < keys.length; ++i) {        if (hashMap[keys[i]]) {            return false;        }    }    return true;}

然而beat 7%，那是当然，毕竟是object，提速的话改成array试试

var checkInclusion = function(s1, s2) {    if (s2.length < s1.length || s2.length === 0) {        return false;    }    const charArr = Array(26).fill(0);    const len = s1.length;    const offset = 'a'.charCodeAt(0);    for (let i = 0; i < len; ++i) {        charArr[s1.charCodeAt(i) - offset]++;        charArr[s2.charCodeAt(i) - offset]--;    }    if (isAllZero(charArr)) {        return true;    }    for (let i = len; i < s2.length; ++i) {        charArr[s2.charCodeAt(i) - offset]--;        charArr[s2.charCodeAt(i-len) -offset]++;        if (isAllZero(charArr)) {            return true;        }    }    return false;};const isAllZero = (charArr) => {    for (let i = 0; i < charArr.length; ++i) {        if (charArr[i]) {            return false;        }    }    return true;}

提速超明显，beat 100%，估计是Array(26).fill(0)和len，offset常量提前算的原因。