题目

迭代法实现子集枚举

func subsets(nums []int) (ans [][]int) {
    n := len(nums)
    for mask := 0; mask < 1<<n; mask++ {
        set := []int{}
        for i, v := range nums {
            if mask>>i&1 > 0 {
                set = append(set, v)
            }
        }
        ans = append(ans, append([]int(nil), set...))
    }
    return
}

• 时间复杂度：O(n×$2^n$)
• 空间复杂度：O(n)

递归法实现子集枚举

func subsets(nums []int) (ans [][]int) {
    set := []int{}
    var dfs func(int)
    dfs = func(cur int) {
        if cur == len(nums) {
            ans = append(ans, append([]int(nil), set...))
            return
        }
        set = append(set, nums[cur])
        dfs(cur + 1)
        set = set[:len(set)-1]
        dfs(cur + 1)
    }
    dfs(0)
    return
}

• 时间复杂度：O(n×$2^n$)
• 空间复杂度：O(n)