222. Count Complete Tree Nodes

题目：
Given a complete binary tree, count the number of nodes.

Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.

解答：

public class Solution {
//学了enum的方法哈哈
public enum Direction {
LEFT, RIGHT
}

public int getDepth(TreeNode root, Direction dir) {
    int depth = 0;
    //这里是从root开始算起，所以求出来的结果是实际depth + 1
    while (root != null) {
        depth++;
        if (dir == Direction.LEFT) {
            root = root.left;
        } else {
            root = root.right;
        }
    }
    return depth;
}

public int countNodes(TreeNode root) {
    if (root == null) return 0;
    int leftDepth = getDepth(root, Direction.LEFT);
    int rightDepth = getDepth(root, Direction.RIGHT);

    if (leftDepth == rightDepth) {
        //1 

关键字：java, root, left, direction

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