MOOC 03_02 List Leaves

队列直接使用的是讲义中的。
本题采用结构数组存放树节点相关信息。
可参考
读取相关的数据进入节点，最后根据队列层序遍历即可从上到下，从左到右得到叶节点的输出。
关键是通过队列这一数据结构实现，根节点入队，，出队时其左右儿子入队。

#include <iostream>
using namespace std;

const int MAXSIZE = 10;

const int QUEUE_INIT_SIZE = 100;
const int ERROR = 0;
const int OK = 1;
const int EMPTY = 1;

typedef int Status;

template <class T>
class SqQueue
{
public:
	SqQueue();
	~SqQueue();
	Status EnQueue(T e);
	Status DeQueue(T &e);
	Status IsEmpty();

private:
	T * base;	//内存空间首地址
	T *front;	//头指针
	T *rear;	//尾指针
	int queueSize;	//队列的长度
};

//初始化顺序队列
template <class T>
SqQueue<T>::SqQueue()
{
	base = new T[QUEUE_INIT_SIZE];
	if (!base)
	{
		cerr << "存储分配失败！" << endl;
	}
	front = rear = base;		//注意此处的赋值顺序,将base赋值给front和rear
	queueSize = QUEUE_INIT_SIZE;
}


template <class T>
SqQueue<T>::~SqQueue()
{
	T *p = front;
	while (p != rear)
	{
		p++;
		delete front;
		front = p;
	}
}
//顺序入队
template <class T>
Status SqQueue<T>::EnQueue(T e)
{
	if (rear - base >= queueSize)
	{
		return ERROR;
	}
	*rear++ = e;	//先赋值，再加指针
	return OK;
}

//顺序队列出队
template <class T>
Status SqQueue<T>::DeQueue(T &e)
{
	if (rear == front)
	{
		return ERROR;
	}
	e = *front++;	//先减指针，再取值
	return OK;
}

template <class T>
Status SqQueue<T>::IsEmpty()
{
	if (front == rear)
	{
		return EMPTY;
	}
	else
	{
		return !EMPTY;
	}
}

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

struct TreeNode T[MAXSIZE];

//建树，返回根节点的值
int BuildTree(struct TreeNode T[])
{
	char cl, cr;
	int check[MAXSIZE];
	int Root = -1;
	int i = 0;
	int N;
	cin >> N;
	if (N)
	{
		for (i = 0; i<N; i++)
		{
			check[i] = 0;	//寻找根节点，此时为0，有指向其的节点则改为1
		}
		for (i = 0; i<N; i++)
		{
			T[i].data = i;
			cin >> cl >> cr;
			if (cl != '-')
			{
				T[i].left = cl - '0';	//字符转数字
				check[T[i].left] = 1;
			}
			else
			{
				T[i].left = -1;
			}

			if (cr != '-')
			{
				T[i].right = cr - '0';
				check[T[i].right] = 1;
			}
			else
			{
				T[i].right = -1;	//置为-1，表示空
			}
		}
		for (i = 0; i<N; i++)
		{
			if (check[i] == 0)
			{
				break;
			}
		}
		Root = i;
		return Root;
	}
}

int main()
{

	int R1 = BuildTree(T);	//根节点
	SqQueue<TreeNode> Q;
	Q.EnQueue(T[R1]);	//根节点进队
	bool flag = true;
	while (!Q.IsEmpty())
	{
		TreeNode temp;
		Q.DeQueue(temp);
		if (temp.left != -1)
		{
			Q.EnQueue(T[temp.left]);
		}
		if (temp.right != -1)
		{
			Q.EnQueue(T[temp.right]);
		}

		if (temp.left == -1 && temp.right == -1 && flag)
		{
			cout << temp.data;
			flag = false;
		}
		else if (temp.left == -1 && temp.right == -1)
		{
			cout << " " << temp.data;
		}

	}

	return 0;
}