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function numDecodings(s: string): number {    const n = s.length;
    let a = 0,        b = 1,        c = 0;    for (let i = 1; i <= n; ++i) {        c = 0;        if (s[i - 1] !== "0") {            c += b;        }        if (            i > 1 &&            s.charAt(i - 2) != "0" &&            Number(s.slice(i - 2, i)) <= 26        ) {            c += a;        }        a = b;        b = c;    }    return c;}export default numDecodings;