0567-permutation-in-string.ts

function checkInclusion(s1: string, s2: string): boolean {
    if (s1.length > s2.length) return false;

    const s1Count = Array(26).fill(0);
    const s2Count = Array(26).fill(0);

    for (let i = 0; i < s1.length; i++) {
        s1Count[s1[i].charCodeAt(0) - 'a'.charCodeAt(0)] += 1;
        s2Count[s2[i].charCodeAt(0) - 'a'.charCodeAt(0)] += 1;
    }

    let matches = 0;
    for (let i = 0; i < 26; i++) {
        if (s1Count[i] == s2Count[i]) {
            matches += 1;
        }
    }

    let l = 0;
    for (let r = s1.length; r < s2.length; r++) {
        if (matches == 26) return true;

        let index = s2[r].charCodeAt(0) - 'a'.charCodeAt(0);
        s2Count[index] += 1;
        if (s1Count[index] == s2Count[index]) {
            matches += 1;
        } else if (s1Count[index] + 1 == s2Count[index]) {
            matches -= 1;
        }

        let index2 = s2[l].charCodeAt(0) - 'a'.charCodeAt(0);
        s2Count[index2] -= 1;
        if (s1Count[index2] == s2Count[index2]) {
            matches += 1;
        } else if (s1Count[index2] - 1 == s2Count[index2]) {
            matches -= 1;
        }
        l += 1;
    }

    return matches == 26;
}