The path to the root node and leaves as target

// recursive it, but on the condition recursion in the end to be a good judge, for example, is the full path to the leaf node, that is to say about the child nodes are empty, and this time root.val == target represents a list found , and then return.

But because I did not use directly on the target-root.val, so in some cases, for example, encountered a null node, we can not directly return, you need to add a value to the list, because then return to the previous level we will remove out of the last element in the list, so every time we have a recursive time to add a list of elements, or return to the previous level when the node elements that do not, this is a point to note,

There is, if it is not a leaf node, and this time root.val> = target, that is, below the else, we can not continue to recursively go directly back on it,

 

** Or you can come directly to the val value to be knocked off, so sometimes you do not need to list the value of adding a insignificant, but this is the end of the target == 0.

 1 import java.util.ArrayList;
 2 /**
 3 public class TreeNode {
 4     int val = 0;
 5     TreeNode left = null;
 6     TreeNode right = null;
 7 
 8     public TreeNode(int val) {
 9         this.val = val;
10 
11     }
12 
13 }
14 */
15 public class Solution {
16     ArrayList<ArrayList<Integer>> res=new ArrayList<>();
17     public ArrayList<ArrayList<Integer>> FindPath(TreeNode root,int target) {
18         ArrayList<Integer> list=new ArrayList<>();
19         if(root==null)
20             return res;
21         helper(root,target,list);
22         return res;
23     }
24     public void helper(TreeNode root, int target,ArrayList<Integer> list)
25     {
26          if(root==null)
27           {
28             list.add(0);
29              return ;
30          }
31         if(root.left==null&&root.right==null)
32         {
33             if(root.val==target)
34             {
35                 list.add(root.val);
36                 res.add(new ArrayList<Integer>(list));
37                 return ;
38             }
39             else
40                 {
41                 list.add(0);
42                  return ;
43          }
44         }
45         if(root.val<target)
46         {
47             list.add(root.val);
48             helper(root.left,target-root.val,list);
49             list.remove(list.size()-1);
50             helper(root.right,target-root.val,list);
51             list.remove(list.size()-1);
52         }
53         else
54             {
55                 list.add(0);
56                 return ;
57         }
58         return ;
59         
60     }
61 }