Solution.ts

function maxSubstringLength(s: string): number {
    const first: number[] = Array(26).fill(-1);
    const last: number[] = Array(26).fill(0);
    const n = s.length;
    for (let i = 0; i < n; ++i) {
        const j = s.charCodeAt(i) - 97;
        if (first[j] === -1) {
            first[j] = i;
        }
        last[j] = i;
    }
    let ans = -1;
    for (let k = 0; k < 26; ++k) {
        const i = first[k];
        if (i === -1) {
            continue;
        }
        let mx = last[k];
        for (let j = i; j < n; ++j) {
            const a = first[s.charCodeAt(j) - 97];
            if (a < i) {
                break;
            }
            const b = last[s.charCodeAt(j) - 97];
            mx = Math.max(mx, b);
            if (mx === j && j - i + 1 < n) {
                ans = Math.max(ans, j - i + 1);
            }
        }
    }
    return ans;
}