JZ24 二叉树中和为某一值的路径

func helper(root *TreeNode ,  expectNumber int, arr []int, ret *[][]int) {
    if root == nil {
        return
    }
    arr = append(arr, root.Val)
    if root.Val == expectNumber && root.Left == nil && root.Right == nil {
        tmp := make([]int, len(arr))
        copy(tmp, arr)
        *ret = append(*ret, tmp)
    }
    helper(root.Left, expectNumber - root.Val, arr, ret)
    helper(root.Right, expectNumber - root.Val, arr, ret)
    
    arr = arr[:len(arr)-1]
}

func pathSum( root *TreeNode,  expectNumber int ) [][]int {
    if root == nil {
        return nil
    }
    var ret [][]int
    helper(root, expectNumber, []int{}, &ret)
    return ret
}