题解 | #二叉树中和为某一值的路径(二)#

要注意java默认是浅拷贝，需要copy.addAll(list);不然结果会为空

另外 list.remove(list.size()-1);删除末尾不需要的元素

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>> res = new ArrayList<>();
    ArrayList<Integer> list = new ArrayList<>();
    
    public ArrayList<ArrayList<Integer>> FindPath(TreeNode root,int expectNumber) {
        if(root == null) return res;
        
        list.add(root.val);
        expectNumber = expectNumber - root.val;
        if(expectNumber == 0 && root.left == null && root.right == null) {
            ArrayList<Integer> copy = new ArrayList<>();
            copy.addAll(list);
            res.add(copy);
        }
        FindPath(root.left,expectNumber);
        FindPath(root.right,expectNumber);
        
        list.remove(list.size()-1);
        
        return res;
    }
}