想了一个简单的面试题

我们有一个数组 ` [5,1,6] `，我们要生成所有的子组合 ` [ [ 5 ], [ 5, 1 ], [ 5, 1, 6 ], [ 5, 6 ], [ 1 ], [ 1, 6 ], [ 6 ] ] `，针对任意数组，该如何求出它的所有子组合呢？

/**
 * @param {number[]} nums
 * @return {number}
 */
var subset = function (nums) {
    let len = nums.length

    function bt(start, arr) {
        if (start >= len) return []

        let subset = []

        for (let i = start; i < len; i++) {
            let n = nums[i]
            let one = [...arr, n]
            subset.push(one)
            subset.push(...bt(i + 1, one))
        }

        return subset
    }

    let subset = bt(0, [])
    console.log(subset)
};

第二种解法。

function subset2(nums) {
    let len = nums.length
    let total = 1 << len
    let subset = []
    let count = 0

    for (let i = 1; i < total; i++) {
        let temp = []
        for (let j = 0; j < len; j++) {
            if ((i >> j) & 1) {
                temp.push(nums[j])
            }
            count++
        }
        subset.push(temp)
    }

    console.log(subset, count)

    // return subset
}

subset2(['a', 'b', 'c'])