【题目20】层序遍历一个棵二叉树

题目：怎样从顶部开始逐层打印二叉树结点数据？请编程。

分析：可以利用队列的先进先出的特性，逐次打印队列中的节点。

                           45

                    21            65

               10    24      50   70

层序遍历的结果： 45，21，65，10，24，50，70

首先45入队，这时队列中有节点元素了，就取出一个来打印，并将

该节点的左子树和右子树分别入队（如果子树不为空的情况下），然后

取下一个先入队的元素打印，并将其左子树和右子树节点入队，一直这

样操作，直到队列为空，打印结束。

 

源代码：

#include <stdio.h>#include <stdlib.h>#define QSIZE 100typedef struct BTree{int value;struct BTree* lChild;struct BTree* rChild;} BTree;//using the feature of the queue,first in first outstruct MyQueue{BTree* queue[QSIZE];int front;int rear;} myQueue; void InitQueue(){myQueue.rear = QSIZE - 1;myQueue.front = myQueue.rear;for(int i = 0;i < QSIZE;i++)myQueue.queue[i] = NULL;}int EnQueue(BTree* newNode){if(myQueue.front >= 1)myQueue.queue[myQueue.front--] = newNode;else return 0;return 1;}BTree* DeQueue(){int t;if(myQueue.front != myQueue.rear){t = myQueue.rear;myQueue.rear--;return myQueue.queue[t];}elsereturn NULL;}void LevelTraversal(BTree** root){InitQueue();BTree* lc = (BTree* ) malloc(sizeof(BTree));BTree* rc = (BTree* ) malloc(sizeof(BTree));BTree* p = (BTree* ) malloc(sizeof(BTree));if((!lc) || (!rc) || (!p)){printf("Out of memery/n");exit(-1); }p = *root;if(!p) { printf("Empty Tree,build it first!/n");}EnQueue(p); // enqueue the root of the treewhile (myQueue.front != myQueue.rear){p = DeQueue();printf("%d ",p->value);lc = p->lChild;rc = p->rChild;if(lc != NULL) EnQueue(lc);if(rc != NULL)EnQueue(rc);} printf("/n");}//recursively insert a tree nodeBTree* Insert(BTree* T, int value){ if(T == NULL) { T = (BTree*)malloc(sizeof(struct BTree)); if( T == NULL) printf("Malloc Failed."); else { T->value = value; T->lChild = T->rChild = NULL; } } else if(value < T->value) T->lChild = Insert(T->lChild,value); else if(value > T->value) T->rChild = Insert(T->rChild, value); return T; }BTree* MakeEmpty(BTree* T){if(T != NULL){MakeEmpty(T->lChild);MakeEmpty(T->rChild);free(T);}return NULL;}int main(){BTree* T = NULL;T = Insert(T,45);T = Insert(T,21);T = Insert(T,65);T = Insert(T,10);T = Insert(T,50); T = Insert(T,70);T = Insert(T,24); LevelTraversal(&T); MakeEmpty(T);return 0;}