全排列 II

func permuteUnique(nums []int) (res [][]int) {
	vis := make([]bool, len(nums))
    n := len(nums)
	sort.Ints(nums)
    var dfs func(nums, path []int, vis []bool) 
    dfs = func(nums, path []int, vis []bool) {
        if n == len(path) {
            res = append(res, append([]int(nil), path...))
            return
        }

        for i := 0; i < len(nums); i++ {
            if vis[i] { //该数已经被使用
                continue
            }
            if i > 0 && nums[i] == nums[i-1] && vis[i-1] == false {
                continue
            }
            vis[i] = true
            dfs(nums, append(path, nums[i]), vis)
            vis[i] = false
        }
    }

    dfs(nums, nil, vis)
	return 
}