MinimumDepthBinaryTreeBFS.java

class MinimumDepthBinaryTreeBFS {
    public int minDepth(TreeNode root) {
        if(root == null) {
            return 0;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        int level = 0;
        while(!queue.isEmpty()) {
            level++;
            int size = queue.size();
            for(int i = 0; i < size; i++) {
                TreeNode node = queue.remove();
                if(node.left == null && node.right == null) {
                    //leaf node
                    return level;
                }
                if(node.left != null) queue.add(node.left);
                if(node.right != null) queue.add(node.right);
            }
        }
        return level;
    }
}