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export default function subsets(nums: number[]): number[][] {    const ans = [];    const n = nums.length;    for (let mask = 0; mask < 2 ** n; ++mask) {        const t = [];        for (let i = 0; i < n; ++i) {            if (mask & (2 ** i)) {                t.push(nums[i]);            }        }        ans.push(t);    }    return ans;}