pta 编程题7 List Leaves

其它pta数据结构编程题请参见：pta

这次的编程作业要求从上到下，从左到右输出一棵树的叶子节点，即树的层序遍历，用队列的方式来实现。

注意enqueue和dequeue函数参数为Queue &q，而不是Queue q，即用引用的方式才能改变实参的值。

#include <iostream>
using namespace std;

struct Node
{
    int left;
    int right;
};

struct Queue
{
    int data[10];
    int first = -1;
    int end = -1;
    int maxSize = 10;
};

int buildTree(Node tree[]);
void enqueue(Queue &q, int i);
int dequeue(Queue &q);
bool empty(Queue q);

int main()
{
    Node tree1[10];
    int root = buildTree(tree1);
    Queue q, leaves;
    int t, cnt = 0;
    enqueue(q, root);
    while (!empty(q))
    {
        t = dequeue(q);
        if (tree1[t].left == -1 && tree1[t].right == -1)
            enqueue(leaves, t);
        if (tree1[t].left != -1) enqueue(q, tree1[t].left);
        if (tree1[t].right != -1) enqueue(q, tree1[t].right);
    }
    while (!empty(leaves))
    {
        if (cnt > 0) cout << " ";
        cout << dequeue(leaves);
        cnt++;
    }
    return 0;
}

int buildTree(Node tree[])
{
    int num, i, root = -1;
    char l, r;
    cin >> num;
    int judgeRoot[10] = {};
    for (i = 0; i < num; i++)
    {
        cin >> l >> r;
        if (l != '-')
        {
            tree[i].left = l - '0';
            judgeRoot[l - '0'] = 1;
        }
        else tree[i].left = -1;
        if (r != '-')
        {
            tree[i].right = r - '0';
            judgeRoot[r - '0'] = 1;
        }
        else tree[i].right = -1;
    }
    for (i = 0; i < num; i++)
    {
        if (judgeRoot[i] == 0) root = i;
    }
    return root;
}

void enqueue(Queue &q, int i)
{
    q.end = (q.end + 1) % 10;
    q.data[q.end] = i;
}

int dequeue(Queue &q)
{
    q.first = (q.first + 1) % 10;
    return q.data[q.first];
}

bool empty(Queue q)
{
    return q.end == q.first;
}