java 222.计算完整树节点（＃）。java

Posted 2021-05-08

public int countNodes(TreeNode root) {
    if (root == null)
        return 0;
    return 1 + countNodes(root.left) + countNodes(root.right)

class Solution {
    public int countNodes(TreeNode root) {
        if (root == null)
            return 0;
        TreeNode left = root, right = root;
        int height = 0;
        while (right != null) {
            left = left.left;
            right = right.right;
            height++;
        }
        if (left == null)
            return (1 << height) - 1;
        return 1 + countNodes(root.left) + countNodes(root.right);
    }
}

class Solution {
    int height(TreeNode root) {
        return root == null ? -1 : 1 + height(root.left);
    }
    public int countNodes(TreeNode root) {
        int nodes = 0, h = height(root);
        while (root != null) {
            if (height(root.right) == h - 1) {
                nodes += 1 << h;
                root = root.right;
            } else {
                nodes += 1 << h-1;
                root = root.left;
            }
            h--;
        }
        return nodes;
    }
}

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private int height(TreeNode root) {
        return root == null ? -1 : 1 + height(root.left);
    }
    public int countNodes(TreeNode root) {
        int h = height(root);
        return h < 0 ? 0 : 
                height(root.right) == h - 1 ? (1 << h) + countNodes(root.right) : 
                                              (1 << (h - 1)) + countNodes(root.left);
    }
}