二叉树的层序遍历，c/c++描述

  按一层一层，从上往下，从左到右的顺序遍历二叉树。称为层序遍历。这里用到了队列。一端插入，另一端删除。对于二叉树链表，我们易于实现纵向访问，从祖先节点，到父母节点，到子孙节点，但对于一个节点来讲，它有多少个同行的兄弟，堂兄弟节点，却是不容易知道的。所以我们要用有记忆功能的循环队列来配合访问二叉树，因为顺序队列里的数组成员可以保存一整行二叉树节点。再把它们逐个输出，在逐个输出队列里本行节点时，确认它们的子节点情况，并也保存在这个队列里。
  完整代码如下：

#include<iostream>
#include<stdio.h>
using namespace std;
#define STACKDEPTH 15
#define QUEUELENTH 15
struct BiTreeNode {
	char value;
	BiTreeNode* leftChild;
	BiTreeNode* rightChild;
};
struct QueueNodes {
	BiTreeNode* nodes[QUEUELENTH];
	int indexHead = 0;
	int indexTail = 0;
};
void createBTree(BiTreeNode *&biTreeRoot,char *&ptChar) {
	struct {
		BiTreeNode* ptsBiTree[STACKDEPTH];
		int indexTop = -1;
	}sequStack;

	BiTreeNode* ptNew = NULL;
	char s ;
	int leftRight;//1 is left   2 is right
	while (*ptChar != '\0') {
		s = *ptChar;
		if ('A' <= s && s <= 'Z') {
			ptNew = new BiTreeNode;
			ptNew->value = s;
			ptNew->leftChild = ptNew->rightChild = NULL;

			if (biTreeRoot == NULL)
				biTreeRoot = ptNew;
			else if (leftRight == 1)
				sequStack.ptsBiTree[sequStack.indexTop]->leftChild = ptNew;
			else if (leftRight == 2)
				sequStack.ptsBiTree[sequStack.indexTop]->rightChild = ptNew;
		}
		else if (s == '(') {
			sequStack.indexTop++;
			sequStack.ptsBiTree[sequStack.indexTop] = ptNew;
			leftRight = 1;
		}
		else if (s == ',')
			leftRight = 2;
		else if (s == ')')
			sequStack.indexTop--;
	
		ptChar++;
	}
}
void displayBTree(BiTreeNode *&biTreeRoot) {   // 本查找方法是先序遍历
	if (biTreeRoot == NULL)
		return;//if binary tree does not exsit,return
	cout << biTreeRoot->value;
	if (biTreeRoot->leftChild != NULL || biTreeRoot->rightChild != NULL) {
		cout << '(';
		displayBTree(biTreeRoot->leftChild);
		if (biTreeRoot->rightChild != NULL) {
			cout << ',';
			displayBTree(biTreeRoot->rightChild);
		}
		cout << ')';
	}
}
void levelOrder(BiTreeNode *&biTreeRoot) {
	if (biTreeRoot == NULL)
		return;
	QueueNodes queue;
	BiTreeNode* pt;
	queue.indexTail++;
	queue.nodes[queue.indexTail] = biTreeRoot;
	while (queue.indexHead != queue.indexTail) {
		queue.indexHead = (queue.indexHead + 1) % QUEUELENTH;
		pt = queue.nodes[queue.indexHead];
		cout << pt->value<<' ';
		
		if (pt->leftChild != NULL) {
			queue.indexTail = (queue.indexTail + 1) % QUEUELENTH;
			queue.nodes[queue.indexTail] = pt->leftChild;
		}
	
		if (pt->rightChild != NULL) {
			queue.indexTail = (queue.indexTail + 1) % QUEUELENTH;
			queue.nodes[queue.indexTail] = pt->rightChild;
		}
	}
}
int main() {
	char array[] = "A(B(D(,G)),C(E,F))";
	char* ptChar = array;  //c++里只能这样分开定义，要不会出错。
	BiTreeNode* biTreeRoot = NULL;

	createBTree(biTreeRoot,ptChar);
	cout << "the char array is :";
	for (int i = 0; array[i] != '\0'; i++)
		cout << array[i];
	cout<< endl<< "binary tree is    :";
	displayBTree(biTreeRoot);

	cout << endl << "level traverse : "; levelOrder(biTreeRoot);

	return 0;
}

  测试结果如下：

对应二叉树为：