dfs

1.要有明确的结束dfs的标志
2.回溯的时候，要恢复现场

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 {
    public ArrayList<ArrayList<Integer>> FindPath(TreeNode root,int sum) {
        ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
        if(root != null)
            dfs(root,sum,ret,new ArrayList<Integer>(),0);
        return ret;
    }
    public void dfs(TreeNode node,int sum,ArrayList<ArrayList<Integer>> ret,ArrayList<Integer> list,int cur){
        cur += node.val;
        list.add(node.val);
        if(cur == sum && node.left == null && node.right == null){
            ArrayList<Integer> ele = new ArrayList<>(list);
            ret.add(ele);
        }
        if(node.left != null){
            dfs(node.left,sum,ret,list,cur);
        }
        if(node.right != null){
            dfs(node.right,sum,ret,list,cur);
        }
        list.remove(list.size() - 1);
        cur -= node.val;
    }
}