A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:

• The left subtree of a node contains only nodes with keys less than or equal to the node's key.
• The right subtree of a node contains only nodes with keys greater than the node's key.
• Both the left and right subtrees must also be binary search trees.

Insert a sequence of numbers into an initially empty binary search tree. Then you are supposed to count the total number of nodes in the lowest 2 levels of the resulting tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤1000) which is the size of the input sequence. Then given in the next line are the N integers in [−10001000] which are supposed to be inserted into an initially empty binary search tree.

Output Specification:

For each case, print in one line the numbers of nodes in the lowest 2 levels of the resulting tree in the format:

n1 + n2 = n

where n1 is the number of nodes in the lowest level, n2 is that of the level above, and n is the sum.

Sample Input:

925 30 42 16 20 20 35 -5 28

Sample Output:

2 + 4 = 6

 

1 #include 
       
         2 #include 
        
          3 #include 
         
           4 #include 
          
            5 #include 
           
             6 using namespace std; 7 int height; 8 struct node{ 9     int data,h,lvl;10     node* l,*r;11 };12 node* newnode(int x){13     node* root = new node;14     root->data=x;15     root->l=NULL;16     root->r=NULL;17     root->h=1;18     return root;19 }20 int geth(node* root){21     if(root==NULL) return 0;22     return root->h;23 }24 void updateh(node* root){25     root->h = max(geth(root->l),geth(root->r))+1;26 }27 void insert(node* &root,int x){28     if(root==NULL) {29         root=newnode(x);30         return;31     }32     if(x>root->data){33         insert(root->r,x);34         updateh(root);35     }36     else if(x<=root->data){37         insert(root->l,x);38         updateh(root);39     }40 }41 int main(){42     int n;43     scanf("%d",&n);44     node* root = NULL;45     for(int i=0;i
            
             h;51 int n1=0,n2=0;52 queue
             
               q;53 root->lvl=1;54 q.push(root);55 while(!q.empty()){56 node* now=q.front();57 q.pop();58 //printf("%d %d\n",now->data,now->lvl);59 if(now->l!=NULL){60 now->l->lvl=now->lvl+1;61 q.push(now->l);62 }63 if(now->r!=NULL){64 now->r->lvl=now->lvl+1;65 q.push(now->r);66 }67 if(now->lvl==height)n1++;68 if(now->lvl==height-1)n2++;69 }70 printf("%d + %d = %d",n1,n2,n1+n2);71 }
             
            
           
          
         
        
       

注意点：二叉搜索树的建立与层序遍历。不过好像做麻烦了，用dfs会更简洁。又好像dfs都不用，可以直接在插入时候加个lvl数组算