# 

## 



## 

[reverse-string](https://leetcode-cn.com/problems/reverse-string/)

>  `char[]` 

```go
func reverseString(s []byte) {
	res := make([]byte, 0)
	reverse(s, 0, &res)
	for i := 0; i < len(s); i++ {
		s[i] = res[i]
	}
}
func reverse(s []byte, i int, res *[]byte) {
	if i == len(s) {
		return
	}
	reverse(s, i+1, res)
	*res = append(*res, s[i])
}
```

[swap-nodes-in-pairs](https://leetcode-cn.com/problems/swap-nodes-in-pairs/)

> 
> ****

```go
func swapPairs(head *ListNode) *ListNode {
    // 
    // 
    return helper(head)
}
func helper(head *ListNode)*ListNode{
    if head==nil||head.Next==nil{
        return head
    }
    // 
    nextHead:=head.Next.Next
    // 
    next:=head.Next
    next.Next=head
    head.Next=helper(nextHead)
    return next
}
```

[unique-binary-search-trees-ii](https://leetcode-cn.com/problems/unique-binary-search-trees-ii/)

>  n 1 ...n 

```go
func generateTrees(n int) []*TreeNode {
    if n==0{
        return nil
    }
    return generate(1,n)

}
func generate(start,end int)[]*TreeNode{
    if start>end{
        return []*TreeNode{nil}
    }
    ans:=make([]*TreeNode,0)
    for i:=start;i F(N) = F(N - 1) + F(N - 2),  N > 1.
>  N F(N)

```go
func fib(N int) int {
    return dfs(N)
}
var m map[int]int=make(map[int]int)
func dfs(n int)int{
    if n < 2{
        return n
    }
    // 
    if m[n]!=0{
        return m[n]
    }
    ans:=dfs(n-2)+dfs(n-1)
    // 
    m[n]=ans
    return ans
}
```

## 

- [ ] [reverse-string](https://leetcode-cn.com/problems/reverse-string/)
- [ ] [swap-nodes-in-pairs](https://leetcode-cn.com/problems/swap-nodes-in-pairs/)
- [ ] [unique-binary-search-trees-ii](https://leetcode-cn.com/problems/unique-binary-search-trees-ii/)
- [ ] [fibonacci-number](https://leetcode-cn.com/problems/fibonacci-number/)