剑指 Offer 34. 二叉树中和为某一值的路径

https://leetcode-cn.com/problems/er-cha-shu-zhong-he-wei-mou-yi-zhi-de-lu-jing-lcof/

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;
//当目标值被减为0，并且到达叶子节点，两个条件同时满足时，题目条件成立
        if(tar == 0 && root.left == null && root.right == null)
            res.add(new LinkedList(path));
        recur(root.left, tar);
        recur(root.right, tar);
        path.removeLast();
    }
}