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[];
     int first = -;
     int end = -;
     int maxSize = ;
 };

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

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

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

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

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

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