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export default function minWindow(s: string, t: string): string {    const need = new Map<string, number>();    for (const c of t) {        need.set(c, (need.get(c) ?? 0) + 1);    }
    let l = 0,        r = 0,        valid = 0;
    let res = "";
    const window = new Map<string, number>();
    while (r < s.length) {        const c = s[r];
        if (need.get(c)) {            // 更新窗口值            window.set(c, (window.get(c) ?? 0) + 1);
            if (window.get(c) == need.get(c)) valid++;
            // valid 不一定是最短的，需要左指针不断右移            while (valid === need.size) {                const cur = s.slice(l, r + 1);                const len = res.length;                res = len === 0 || r + 1 - l < len ? cur : res;
                // 找到一个满足条件后，更新左指针直至其指向t中字符                do {                    const d = s[l];                    if (need.get(d)) {                        if ((window.get(d) ?? 0) == (need.get(d) ?? 0)) {                            valid--;                        }                        window.set(d, (window.get(d) ?? 0) - 1);                    }                    l++;                } while (!need.get(s[l]) && l <= r);            }        }
        // 当前区间不存在符合条件的子串时，右指针才更新        r++;    }
    return res;}