Minimum Depth of Binary Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    
    public int minDepth(TreeNode root) {
        
        if(root==null){
            return 0;
        }
        
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        
        queue.add(root);
        
        int level = 1;
        int minDepth = 1000000000;
        
        while(!queue.isEmpty()){
            
            int size = queue.size();
            
            for(int i=0;i<size;i++){
                TreeNode node = queue.remove();
                
                if(node!=null && node.left==null && node.right==null){
                    if(minDepth>level){
                        return level;
                    }
                   
                }else{
                    if(node.left!=null){
                        queue.add(node.left);    
                    }
                    if(node.right!=null){
                        queue.add(node.right);
                    }
                }
                
            }
            level ++;
        }
        
        return minDepth;
    }
    
}