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!
");
        return NULL;
    }
    root->left=NULL;
    root->right=NULL;
    printf("Input the data of root!
");
    scanf("%d",&root->data);
    printf("Root created!
");
    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
");
        return ;
    }
    switch(select){
        case 1:
            if(root->left){
                printf("The root has left subtree!
");
                return ;
            }else{
                root->left=node;
                break;
            }
        case 2:
                if(root->right){
                printf("The root has right subtree!
");
                return ;
            }else{
                root->right=node;
                break;
            }
        default:
            printf("The input of select is wrong!
");
    }
}

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
",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
",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
",root->data);
}

6、求二叉树的深度

int lengthTree(TreeNode *root){
    int lenLeft,lenRight;
    if(NULL==root)
    return 0;
    else{
        lenLeft=lengthTree(root->left);
        lenRight=lengthTree(root->right);
        if(lenLeft<lenRight)
        return lenRight+1;
        else
        return lenLeft+1;
    }
}

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

9、二叉树的层次遍历

void levelFind(TreeNode * root){
    TreeNode *node;
    TreeNode *Queue[MAX];
    int head,tail;
    head=tail=0;
    if(root==NULL){
        printf("Queue is empty!
");
        return ;
    }
    if((tail+1)%MAX!=head)
        Queue[tail++]=root;
    else
        printf("Queue is full!
");
    if(head!=tail)
        node=Queue[head++];
    else
        printf("Queue is empty!
");
    printf("The bintree level find is: 
");
    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!
");
            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!
");
        scanf("%d",&n);
        switch(n){
            case 0:
                break;
            case 1:
                if(NULL==root)
                root=creatRoot();
                else
                printf("The root is exist!
");
                break;
            case 2:
                addNode(root);
                break;
            case 3:
                DLR(root);
                break;
            case 4:
                LDR(root);
                break;
            case 5:
                LRD(root);
                break;
            case 6:
                levelFind(root);
                break;
            case 7:
            printf("the depth of tree is %d
",lengthTree(root));
                break;
        }
    }while(n!=0);
    clearTree(root);
    printf("Tree are cleared all!
");
    getch();
    return 0;
    
}