LeetCode OJ

这两道题用递归的解法都很简单，只是稍有不同。

下面是AC代码：

 /**
     * 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.
     * @param root
     * @return
     */
    public int minDepth(TreeNode root){
        //the boundary condition
        if(root == null)
            return 0;
        return minDepthRec(root);
    }
    private int minDepthRec(TreeNode root){
        if(root == null)
            return 0;
        if(root.left == null && root.right == null)
            return 1;
        //the condition judged here is very important here
        if(root.left == null)
            return minDepthRec(root.right)+1;
        if(root.right == null)
            return minDepthRec(root.left)+1;
        return Math.min(minDepthRec(root.left), minDepthRec(root.right))+1;
    }

/**
     * 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.
     * @param root
     * @return
     */
    public int maxDepth(TreeNode root){
        if(root == null)
            return 0;
        if(root.left == null && root.right == null)
            return 1;
        return Math.max(maxDepth(root.left), maxDepth(root.right))+1;
    }