combination:
这个是典型的combination做法
dfs，注意中间结果一定要copy到新的变量中，不然会得到空值
var ans [][]int
func subsets(nums []int) [][]int {
ans = [][]int{}
cur := []int{}
for i := 0; i <= len(nums); i++ {
dfs(nums, i, 0, cur)
}
return ans
}
func dfs(nums []int, n, s int, cur []int) {
if len(cur) == n {
//这里一定要拷贝
tmp := make([]int, n)
copy(tmp, cur)
ans = append(ans, tmp)
return
}
for i := s; i < len(nums); i++ {
cur = append(cur, nums[i])
dfs(nums, n, i+1, cur)
cur = cur[:len(cur)-1]
}
}
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