递归的应用--求二叉树最大深度和最小深度

【求最大深度】Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

这里说的最大深度是指最深叶子节点到根节点的路径长度

<span style="font-size:18px;">	 public static int maxDepth(TreeNode root) {
		 if(root==null)return 0;
		 if(root.right==null && root.left==null)return 1;
		 else return 1+Math.max(maxDepth(root.right), maxDepth(root.left));
	    }</span>

【求最小深度】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.

这里说的最小深度是指最浅叶子节点到根节点的路径长度，求最小深度相对最大深度来讲要麻烦一点点。

<span style="font-size:18px;"> public static int minDepth(TreeNode root) {
		 if(root==null)return 0;
		 if(root.right==null && root.left==null)//没有子节点
		 {
			 return 1;
		 }
		 else if(root.right!=null && root.left!=null)//左右儿子都存在
		 {
			return Math.min( 1+minDepth(root.left),1+minDepth(root.right));

		 }
		 else if(root.right==null)//只有左儿子
		 {
			 return 1+minDepth(root.left);
		 }
		 else
		 {
			 return 1+minDepth(root.right);//只有右儿子
		 }
	 }</span>