Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

DFS:

public class Solution {
    //Time: O(n)
    int min = Integer.MAX_VALUE;
    public int minDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        getMin(root, 1);
        return min;
    }
    
    private void getMin(TreeNode root, int depth) {
        if (root.left == null && root.right == null) {
            min = Math.min(min, depth);
        }
        
        if (root.left != null) {
            getMin(root.left, depth + 1);
        }
        if (root.right != null) {
            getMin(root.right, depth + 1);
        }
    }
}

BFS:

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