树-------完全二叉树结点数



完全二叉树结点数

给定一棵完全二叉树的头节点head，返回这棵树的节点个数。如果完全二叉树的节点数为N，请实现时间复杂度低于O(N)的解法。 

/**

public class TreeNode {

    int val = 0;

    TreeNode left = null;

    TreeNode right = null;

 

    public TreeNode(int val) {

        this.val = val;

 

    }

}*/

public class Solution {

    public int nodeNum(TreeNode head) {

        if(head==null) return 0;

        TreeNode tempLeft=head.left,tempRight=head.right;

        if(tempLeft==null) return 1;

        if(tempRight==null) return 2;

        int leftHigt=1,rightHigh=1;

        while(tempLeft.left!=null) {

            tempLeft=tempLeft.left;

            leftHigt++;

        }

        while(tempRight.left!=null) {

            tempRight=tempRight.left;

            rightHigh++;

        }

        if(rightHigh==leftHigt)return (1<<leftHigt)+nodeNum(head.right);

        else return (1<<rightHigh)+nodeNum(head.left);

    }

}