[leetcode]Path Sum II - java 回溯法

/**

 * Definition for binary tree

 * 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>> results  = new ArrayList<List<Integer>>();

        if(root==null){

            return results;

        }

        List<Integer> result = new ArrayList<Integer>();

        result.add(root.val);

        eSum(root, root.val, sum, result, results);

        return results;

    }



    private void eSum(TreeNode node, int s, int sum, List<Integer> result, List<List<Integer>> results){

        if(node.left==null && node.right==null){

            if(s == sum){

                List<Integer> r = new ArrayList<Integer>();

                for(Integer e : result){

                    r.add(e);

                }

                results.add(r);

            }

            return;

        }

        if(node.left != null){

            s+=node.left.val;

            result.add(node.left.val);

            int length = result.size()-1;

            eSum(node.left, s, sum, result, results);

            s-=node.left.val;

            result.remove(length);

        }

        if(node.right != null){

            s+=node.right.val;

            result.add(node.right.val);

            int length = result.size()-1;

            eSum(node.right, s, sum, result, results);

            result.remove(length);

        }

    }

}