LeetCode35|完全二叉树的节点个数

说明：

完全二叉树的定义如下：在完全二叉树中，除了最底层节点可能没填满外，其余每层节点数都达到最大值，并且最下面一层的节点都集中在该层最左边的若干位置。若最底层为第 h 层，则该层包含 1~ 2h 个节点。

示例:

输入: 
    1
   / \
  2   3
 / \  /
4  5 6

输出: 6

 

import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
import java.util.List;

public class CountNodesTest {
    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(1);
        TreeNode t2 = new TreeNode(2);
        TreeNode t3 = new TreeNode(3);
        TreeNode t4 = new TreeNode(4);
        TreeNode t5 = new TreeNode(5);
        TreeNode t6 = new TreeNode(6);
        t1.left = t2;
        t1.right = t3;
        t2.left = t4;
        t2.right = t5;
        t3.left = t6;
        int countNodes = countNodes(t1);
        System.out.println("countNodes = " + countNodes);

        int count = countNodes2(t1);
        System.out.println("count = " + count);
    }

    public static int countNodes(TreeNode root) {
        if (root == null) {
            return 0;
        }
        Deque<TreeNode> deque = new LinkedList<>();
        deque.add(root);
        List<Integer> list = new ArrayList<>();
        while (!deque.isEmpty()) {
            int size = deque.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = deque.poll();
                list.add(node.val);
                if (node.left != null) {
                    deque.add(node.left);
                }
                if (node.right != null) {
                    deque.add(node.right);
                }
            }

        }
        return list.size();
    }

    public static int countNodes2(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftLevel = countLevel(root.left);
        int rightLevel = countLevel(root.right);
        if (leftLevel == rightLevel) {
            return countNodes(root.right) + (1 << leftLevel);
        } else {
            return countNodes(root.left) + (1 << rightLevel);
        }
    }

    private static int countLevel(TreeNode root) {
        int level = 0;
        while (root != null) {
            level++;
            root = root.left;
        }
        return level;
    }
}