2022-03-02 II 050. 向下的路径节点之和

回溯和深度遍历
Go版本：

func pathSum(root *TreeNode, targetSum int)(res int) {

   
    if root==nil{
        return  
    }
    res=rootSum(root,targetSum)
    res+=pathSum(root.Left,targetSum)
    res+=pathSum(root.Right,targetSum)

 return ;

}
func  rootSum(root *TreeNode,targetSum int)(res int){
    if root==nil{
        return 0
    }
    value:=root.Val
    if value==targetSum{
        res++;
    }

   res+= rootSum(root.Left,targetSum-value)
    res+=rootSum(root.Right,targetSum-value)
    return ;

}