已知一棵完全二叉树，求其节点的个数 要求：时间复杂度低于O(N)，N为这棵树的节点个数

 package my_basic.class_4; public class Code_08_CBTNode {
     // 完全二叉树的节点个数 复杂度低于O(N)     public static class Node {
         int value;
         Node left;
         Node right;         public Node(int value) {
             this.value = value;
         };
     }     public static int nodeNum(Node head) {
         if (head == null) {
             return 0;
         }
         return bs(head, 1, mostLeftLevel(head, 1));
     }     public static int bs(Node node, int level, int h) {
         if (level == h) {
             return 1;
         }
         if (mostLeftLevel(node.right, level + 1) == h) {
             System.out.println("递归中右 = h --："+(1 << (h - level) + bs(node.right, level + 1, h)));
             return (1 << (h - level)) + bs(node.right, level + 1, h);
         } else {
             System.out.println("递归中右 != h："+(1 << (h - level - 1) + bs(node.left, level + 1, h)));
             return (1 << (h - level - 1)) + bs(node.left, level + 1, h);
         }
     }     public static int mostLeftLevel(Node node, int level) {
         while (node != null) {
             level++;
             node = node.left;
         }
         return level - 1;
     }     //打印二叉树
     public static void printTree(Node head) {
         System.out.println("Binary Tree:");
         printInOrder(head, 0, "H", 17);
         System.out.println();
     }     public static void printInOrder(Node head, int height, String to, int len) {
         if (head == null) {
             return;
         }
         printInOrder(head.right, height + 1, "v", len);
         String val = to + head.value + to;
         int lenM = val.length();
         int lenL = (len - lenM) / 2;
         int lenR = len - lenM - lenL;
         val = getSpace(lenL) + val + getSpace(lenR);
         System.out.println(getSpace(height * len) + val);
         printInOrder(head.left, height + 1, "^", len);
     }     public static String getSpace(int num) {
         String space = " ";
         StringBuffer buf = new StringBuffer("");
         for (int i = 0; i < num; i++) {
             buf.append(space);
         }
         return buf.toString();
     }     public static void main(String[] args) {
         Node head = new Node(1);
         head.left = new Node(2);
         head.right = new Node(3);
         head.left.left = new Node(4);
         head.left.right = new Node(5);
         head.right.left = new Node(6);
         System.out.println(nodeNum(head)); //        printTree(head);     }
 }