[LeetCode] 111. Minimum Depth of Binary Tree

class Solution {
    public int minDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        
        int level = 1;
        
        while (!queue.isEmpty()) {
            int size = queue.size();
            
            for (int i = 0; i < size; i++) {
                TreeNode curNode = queue.poll();
                
                if (curNode.left == null && curNode.right == null) {
                    return level;
                }
                
                if (curNode.left != null) {
                    queue.offer(curNode.left);
                }
                
                if (curNode.right != null) {
                    queue.offer(curNode.right);
                }
                
            }
            
            level++;
        }
        
        return level;
    }
}