二叉树中和为某一值的路径

得到结果路径后需要用temp复制path的内容，并存储在res中，否则res中存储的只是引用

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    List<List<Integer>> res = new ArrayList<>();
    List<Integer> path = new ArrayList<>();

    public List<List<Integer>> findPath(TreeNode root, int sum) {
        dfs(root, sum);
        return res;
    }

    private void dfs(TreeNode root, int sum) {
        if (root == null)
            return;
        sum -= root.val;
        path.add(root.val);
        if (root.left == null && root.right == null && sum == 0){
            List<Integer> temp = new ArrayList<>(path);
            res.add(temp);
        }
        dfs(root.left, sum);
        dfs(root.right, sum);
        path.remove(path.size() - 1);
    }
}