111. 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.

题目含义：获得二叉树的最小高度

方法一：dfs

    private int findMinDepth(TreeNode node)
    {
        if (node == null) return 0;
        if (node.left == null&&node.right==null) return 1;
        
        if (node.left == null) return findMinDepth(node.right)+1;
        else if (node.right == null) return findMinDepth(node.left)+1;
        else return 1+Math.min(findMinDepth(node.left),findMinDepth(node.right));
    }
    
    public int minDepth(TreeNode root) {
        if (root == null) return 0;
        return findMinDepth(root);        
    }
}

 方法二：BFS

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