113. Path Sum II

import java.util.ArrayList;
import java.util.List;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */


public class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
       
        List<List<Integer>> res=new ArrayList<List<Integer>>();
        
        if(root==null)
            return res;
        
        List<Integer> temp=new ArrayList<Integer>();
        
        DFS(root,sum,0,temp,res);
        
        return res;
    }
    public void DFS(TreeNode root,int sum,int total,List<Integer> temp,List<List<Integer>> res)
    {
        //将当前节点添加进去
        temp.add(root.val);
        
        total+=root.val;
        
        //如果此时是已经是叶子节点
        if(root.left==null&&root.right==null)
        {
            if(sum==total)
            {
                //已经找到目标路径
                res.add(new ArrayList<Integer>(temp));
            }
            return ;
        }
        if(root.left!=null)
        {
            DFS(root.left,sum,total,temp,res);
            temp.remove(temp.size()-1);
        }
        if(root.right!=null)
        {
            DFS(root.right,sum,total,temp,res);
            temp.remove(temp.size()-1);
        }
    }
}