LeetCode 222. Count Complete Tree Nodes(二分+位运算)

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int countNodes(TreeNode* root) {
        
        if(root==NULL)
            return 0;
        
        int h=0;
        GetHeight(root,h);
        if(h==0)
            return 1;
        
        int l =0;
        int r = (1<<h)-1;
        
        while(l<=r)
        {
            int mid = (l+r)/2;
            if(DFS(root,mid,1<<(h-1)))
            {
                l = mid+1;
            }
            else
            {
                r = mid-1;
            }   
        }
        
        return (1<<h)+r;
 
    }
    
    void GetHeight(TreeNode* root,int& h)
    {
        if(root->left!=NULL)
        {
            GetHeight(root->left,++h);
        }
    }
    
    int DFS(TreeNode* root,int x,int y)
    {
        if(y==0)
            return 1;
        if(x&y)
        {
            if(root->right==NULL)
                return 0;
            else
                return DFS(root->right,x,y>>1);
        }
        else
        {
            if(root->left==NULL)
                return 0;
            else
                return DFS(root->left,x,y>>1);
        }
    }
};