二叉树各种相关操作(建立二叉树、前序、中序、后序、求二叉树的深度、查找二叉树节点，层次遍历二叉树等）（C语言版)

将二叉树相关的操作集中在一个实例里，有助于理解有关二叉树的相关操作：

1、定义树的结构体：

 typedef struct TreeNode{
     int data;
     struct TreeNode *left;
     struct TreeNode *right;
 }TreeNode;

2、创建根节点：

 TreeNode *creatRoot(){
     TreeNode * root =(TreeNode *)malloc(sizeof(TreeNode));
     if(NULL==root){
         printf("CreatRoot is failing!\n");
         return NULL;
     }
     root->left=NULL;
     root->right=NULL;
     printf("Input the data of root!\n");
     scanf("%d",&root->data);
     printf("Root created!\n");
     return root;
 } 

3、申请了空间一定要记得释放空间，否则后果不堪设想

 void clearTree(TreeNode * root){
     if(root){
         clearTree(root->left);
         clearTree(root->right);
         free(root);
     }
 }

4、选择插入的节点是根节点的左孩子还是右孩子

 void addSubTreeNode(TreeNode* root,TreeNode*node,int select){
     if(NULL==root){
         printf("Root is NULL\n");
         return ;
     }
     switch(select){
         case :
             if(root->left){
                 printf("The root has left subtree!\n");
                 return ;
             }else{
                 root->left=node;
                 break;
             }
         case :
                 if(root->right){
                 printf("The root has right subtree!\n");
                 return ;
             }else{
                 root->right=node;
                 break;
             }
         default:
             printf("The input of select is wrong!\n");
     }
 }

5、二叉树的前序、中序、后序遍历

 void DLR(TreeNode * root){
     if(NULL==root)
     return;
     printf("The First root input %d\n",root->data);
     DLR(root->left);
     DLR(root->right);
 }

 void LDR(TreeNode * root){
     if(NULL==root)
     return;
     LDR(root->left);
     printf("The Middle root input %d\n",root->data);
     LDR(root->right);
 }

 void LRD(TreeNode * root){
     if(NULL==root)
     return;
     LRD(root->left);
     LRD(root->right);
     printf("The Last root input %d\n",root->data);
 }

6、求二叉树的深度

 int lengthTree(TreeNode *root){
     int lenLeft,lenRight;
     if(NULL==root)
     return ;
     else{
         lenLeft=lengthTree(root->left);
         lenRight=lengthTree(root->right);
         if(lenLeft<lenRight)
         return lenRight+;
         else
         return lenLeft+;
     }
 }

7、查找节点，这里是为了初始化构建二叉树时选择的函数，目的是找出你要插入节点的父亲节点

 TreeNode *treeFind(TreeNode *node,int number){
     TreeNode *p;
     if(NULL==node)
     return NULL;
     else{
         if(node->data==number){
             return node;
         }else{
             if(p=treeFind(node->left,number)){
                 printf("Parent found!\n");
                 return p;
             }

             else if(p=treeFind(node->right,number)){
                 printf("Parent found!\n");
                 return p;
             }
             else
             return NULL;
         }
     }
 }

8、找到父亲节点后，选择是插入做孩子还是右孩子

 void addNode(TreeNode *root){
     TreeNode *node,*parent;
     int number,select;
     printf("Please input the parent data!\n");
     scanf("%d",&number);
     parent=treeFind(root,number);
     if(NULL==parent){
         printf("parent is not found!\n");
         return ;
     }
             printf("Please choice the operation: 0 Exit; 1 insert left subtree; 2 insert right subtree!\n");
             scanf("%d",&select);
             if(select==)
             return ;
             if(node=(TreeNode*)malloc(sizeof(TreeNode))){
                 printf("Please input the data of BinTreeData that you want to insert!\n");
                 scanf("%d",&node->data);
                 node->left=NULL;
                 node->right=NULL;
                 switch(select){
                     case :
                         addSubTreeNode(parent,node,);
                         break;
                     case :
                         addSubTreeNode(parent,node,);
                         break;
                 }
             }
 }

9、二叉树的层次遍历

 void levelFind(TreeNode * root){
     TreeNode *node;
     TreeNode *Queue[MAX];
     int head,tail;
     head=tail=;
     if(root==NULL){
         printf("Queue is empty!\n");
         return ;
     }
     if((tail+)%MAX!=head)
         Queue[tail++]=root;
     else
         printf("Queue is full!\n");
     if(head!=tail)
         node=Queue[head++];
     else
         printf("Queue is empty!\n");
     printf("The bintree level find is: \n");
     while(NULL!=node){
         printf("%d  ",node->data);
         if(node->left!=NULL){
             Queue[tail++]=node->left;
         }
         if(node->right!=NULL){
             Queue[tail++]=node->right;
         }
         if(head==tail){
             printf("Queue is empty!\n");
             return;
         }
         node=Queue[head++];
     }
 }

10、主函数

 int main(){
     TreeNode *root=NULL;
     int n;
     do{
         printf("1 set root, 2 addNode, 3 the First root input, 4 the Middle root input, 5 the last root input, 6 according to level find, 7 caculate the depth, 0 exit!\n");
         scanf("%d",&n);
         switch(n){
             case :
                 break;
             case :
                 if(NULL==root)
                 root=creatRoot();
                 else
                 printf("The root is exist!\n");
                 break;
             case :
                 addNode(root);
                 break;
             case :
                 DLR(root);
                 break;
             case :
                 LDR(root);
                 break;
             case :
                 LRD(root);
                 break;
             case :
                 levelFind(root);
                 break;
             case :
             printf("the depth of tree is %d\n",lengthTree(root));
                 break;
         }
     }while(n!=);
     clearTree(root);
     printf("Tree are cleared all!\n");
     getch();
     return ;

 }