从上到下打印二叉树

Posted 2021-06-12 HelloCoding08

从上到下打印出二叉树的每个节点，同一层的节点按照从左到右的顺序打印。 

例如，给定如下二叉树: root = [ 3,  5 , 1,  6,  2, 9, 8, null, null,7 , 4 ]

返回： [3， 5， 1， 6， 2， 9， 8， 7， 4]

相当于二叉树的层次遍历

#include <stdio.h>#include <stdlib.h>
#define MAXSIZE 20//树的值的类型typedef int TreeElem;//树的结点类型typedef struct tree_node TreeNode;//队列结点类型typedef struct queue_node QueueNode;//队列元素类型typedef struct tree_node* QueueElem;typedef struct tree_node* Tree;typedef struct queue_node* Queue;
struct tree_node { TreeElem elem; TreeNode* lchild; TreeNode* rchild;};struct queue_node { int front; int rear; QueueElem elem[MAXSIZE];};//创建队列Queue create_queue () { Queue queue = (Queue)malloc(sizeof(QueueNode)); queue->front = 0; queue->rear = 0; return queue;}//判队列是否为空int is_empty (Queue queue) { if (queue->front == queue->rear) { return 1; } return 0;}//判队列是否为满int is_full (Queue queue) { if ((queue->rear + 1) % MAXSIZE == queue->front) { return 1; } return 0;}//进队列int en_queue (Queue queue, QueueElem elem) { if (is_full(queue)) { return 0; } queue->elem[queue->rear] = elem; queue->rear = (queue->rear + 1) % MAXSIZE; return 1;}//出队列int de_queue (Queue queue, QueueElem* elem) { if (is_empty(queue)) { return 0; } *elem = queue->elem[queue->front]; queue->front = (queue->front + 1) % MAXSIZE; return 1;}//得到队首的元素int peek_queue (Queue queue, QueueElem* elem) { if (is_empty(queue)) { return 0; } *elem = queue->elem[queue->front]; return 1;}//队列的大小int queue_size (Queue queue) { if (is_empty(queue)) { return 0; } int size = (queue->rear + MAXSIZE - queue->front) % MAXSIZE; return size;}//清空队列void clear_queue (Queue queue) { queue->front = 0; queue->rear = 0;}//创建树Tree create_tree (FILE* fp) { Tree tree; TreeElem elem; fscanf(fp, "%d", &elem); if (0 == elem) { return NULL; } else { tree = (Tree)malloc(sizeof(TreeNode)); tree->elem = elem; tree->lchild = create_tree(fp); tree->rchild = create_tree(fp); } return tree;}
int get_max(int a, int b) { return a > b ? a : b;}//计算树的结点的个数int count_node (Tree tree) { if (tree == NULL) { return 0; } //左孩子 + 右孩子 + 树根 int count = count_node(tree->lchild) + count_node(tree->rchild) + 1; return count;}//树的层次遍历int* level_order (Tree tree, int* size) { //计算出结点的个数    int count = count_node(tree); int* result = (int*)malloc(sizeof(int) * count); //结果的索引 int index = 0; //初始化数据，防止脏数据 for (int i = 0; i < count; i++) { result[i] = -1; } //创建队列 Queue queue = create_queue(); //把根节点加入队列 en_queue(queue, tree);    //用于出队列元素 QueueElem de_elem; while (!is_empty(queue)) { //出队列 de_queue(queue, &de_elem); //加入到结果数组中 result[index++] = de_elem->elem;        //左孩子不为空，把左孩子加入队列 if (de_elem->lchild != NULL) { en_queue(queue, de_elem->lchild); } //同理 if (de_elem->rchild != NULL) { en_queue(queue, de_elem->rchild); } } //释放内存 free(queue); //把result的长度带出去 *size = index; return result;}
void show (int* result, int size) { for (int i = 0; i < size; i++) { printf("%d\t", result[i]); } printf("\n");}
int main () { char path[] = "./demo.txt"; FILE* fp = fopen(path, "r"); if (fp == NULL) { perror("fopen error"); exit(-1); } Tree tree = create_tree(fp); fclose(fp); int size = 0; int* result = level_order(tree, &size); show(result, size); return 0;}

demo.txt

‍