var subsets = function(nums) {
    let answer = [];
    let answers = [];
    function backtrack(index, start){
        if(index <= nums.length)answers.push([...answer]);
        for(let i = start; i <= nums.length - 1; i++){
            answer.push(nums[i]);
            backtrack(index + 1, i + 1);
            answer.pop()
        }
    }
    backtrack(0, 0);
    return answers;
};