LeetCode#113. Path Sum II

• 题目：找出所有从根节点到叶子节点的路径，使得路径节点值之和等于sum
• 难度：Medium
• 思路：先序遍历二叉树，将当前结果加入结果集tmpList中，遍历的过程中，不断更新sum，直到sum等于node.val
• 代码：

public class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> result = new ArrayList<>();
        if(root == null){
            return result;
        }
        helper(result, new ArrayList<>(), sum, root);
        return result;
    }
    public void helper(List<List<Integer>> list, List<Integer> tmp, int sum, TreeNode node){
        tmp.add(node.val);

        if(node.val == sum  && node.left == null && node.right == null){
            list.add(tmp);
            return;
        }

        if(node.left != null){
            helper(list, new ArrayList<>(tmp), sum-node.val, node.left);
        }
        if(node.right != null){
            helper(list, new ArrayList<>(tmp), sum-node.val, node.right);
        }
    }
}