括号生成

func generateParenthesis(n int) []string {
    list := make([]string,0)
    helper(n,n,"",list)
    return list // []
}
 
func helper(left int,right int,str string,list []string) {
    if right == 0 {
        // 不会影响到外部,append在底层会创建一个新的list来添加，添加以后再把新的list返回，但返回的结果不会影响到实参
        list = append(list,str)
        return
    }
    if left==right{
        str1 := str + "("
        helper(left-1,right,str1,list)
    }else{
        if left > 0{
            str1 := str + "("
            helper(left-1,right,str1,list)
        }
        str2 := str + ")"
        helper(left,right-1,str2,list)
    }
} 

func generateParenthesis(n int) []string {
    list := make([]string,0)
    helper(n,n,"",&list)
    return list // []
}


func helper(left int,right int,str string,list *[]string) {
    if right == 0 {
        // 通过*list添加可以影响到外部，相当于把generateParenthesis中的list指向改变了
        *list = append(*list,str)
        return
    }
    if left==right{
        str1 := str + "("
        helper(left-1,right,str1,list)
    }else{
        if left > 0{
            str1 := str + "("
            helper(left-1,right,str1,list)
        }
        str2 := str + ")"
        helper(left,right-1,str2,list)
    }
} 

func generateParenthesis(n int) []string {
    list2 := make([]string,1)
    test2(list2)
    return list2 //["()()"]
}
func test2(list1 []string) {
    // 直接修改会影响外部,前提是list1有这样的空间下标
    list1[0] = "()()"
}

func generateParenthesis(n int) []string {
    list := make([]string,0)
    test(list)
    return list //[]
}
func test(list []string) {
    // 通过append添加的结果不会影响外部
    list = append(list,"()()","()()","()()")
}

func generateParenthesis(n int) []string {
    list := make([]string,0)
    test3(&list)
    return list //[“()()”]
}
func test3(listptr *[]string){
    // 会影响到外部,修改的是实参的指向
    *listptr = append(*listptr,"()()")
}