Minimum Depth of Binary Tree

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int minDepth(TreeNode root) {
int depth = 0;

if (root == null) {
return depth;
}

Queue<TreeNode> current = new LinkedList<TreeNode>();
Queue<TreeNode> next = new LinkedList<TreeNode>();
Queue<TreeNode> temp;

current.offer(root);

while (true) {
depth++;
while (!current.isEmpty()) {
TreeNode node = current.poll();

if (node.left == null && node.right == null) {
return depth;
}
if (node.left != null) {
next.offer(node.left);
}
if (node.right != null) {
next.offer(node.right);
}
}
temp = current;
current = next;
next = temp;
}
}
}