剑指 Offer 34. 二叉树中和为某一值的路径

输入一棵二叉树和一个整数，打印出二叉树中节点值的和为输入整数的所有路径。从树的根节点开始往下一直到叶节点所经过的节点形成一条路径。

示例:
给定如下二叉树，以及目标和 target = 22，

              5
             / 
            4   8
           /   / 
          11  13  4
         /      / 
        7    2  5   1

返回:

[
   [5,4,11,2],
   [5,8,4,5]
]

解法：回溯法

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    LinkedList<List<Integer>> res = new LinkedList<>();
    LinkedList<Integer> path = new LinkedList<>(); 
    public List<List<Integer>> pathSum(TreeNode root, int target) {

         recur(root,target);
         return res;
    }
    void recur(TreeNode root,int tar)
    {
       if(root == null) return ;
       path.add(root.val);
       tar -= root.val;
       if(tar ==0 && root.left == null && root.right == null)
       {
         res.add(new LinkedList(path));
       }
       recur(root.left,tar);
       recur(root.right,tar);
       path.removeLast();
    }
}