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function lengthOfLongestSubstring(s: string): number {    const occ = new Set();    let right = -1;    let ans = 0;    const n = s.length;    for (const i of Array.prototype.keys.call(s)) {        if (i !== 0) {            occ.delete(s[i - 1]);        }        while (right + 1 < n && !occ.has(s[right + 1])) {            occ.add(s[right + 1]);            right++;        }        ans = Math.max(ans, right - i + 1);    }    return ans;}export default lengthOfLongestSubstring;