递归：DFS

Java

import java.util.ArrayList;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {
    ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
    ArrayList<Integer> list = new ArrayList<>();
    public ArrayList<ArrayList<Integer>> FindPath(TreeNode root, int target) {
        if (root != null){
            list.add(root.val);
            target = target - root.val;
            //递归到叶节点
            if (root.left == null && root.right == null && target == 0)
                ret.add(new ArrayList<>(list));            
            FindPath(root.left, target);      //递归左子树
            FindPath(root.right, target);    //递归右子树
            list.remove(list.size() - 1); //如果叶节点不等target，就删除这个节点
        }
        return ret;
    }
}