(LeetCode)二叉树中和为某一值的路径

原体如下：

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.
For example:
Given the below binary tree and 

sum
= 22

,

5
/ \
4   8
/   / \
11  13  4
/  \      \
7    2      1

return true, as there exist a root-to-leaf path 

5->4->11->2

 which sum is 22.
我的代码：
public class Solution {
public boolean mark = false;
public boolean hasPathSum(TreeNode root, int sum) {
if (root == null) {
return false;
}
Stack<Integer> path = new Stack<Integer>();
int currentSum = 0;
findPath(root, sum, path, currentSum);
return mark;
}
public void findPath(TreeNode root, int sum, Stack<Integer> path, int currentSum)
{
currentSum += root.val;
path.push(root.val);
boolean isLeaf = root.left==null&&root.right==null;
if(currentSum==sum&&isLeaf)
{
mark = true;
}
if(root.left != null)
{
findPath(root.left,sum,path,currentSum);
}
if(root.right != null)
{
findPath(root.right,sum,path,currentSum);
}

path.pop();
}
}