PAT 甲级 1099 Build A Binary Search Tree

1099 Build A Binary Search Tree （30 point(s)）

A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:

• The left subtree of a node contains only nodes with keys less than the node's key.
• The right subtree of a node contains only nodes with keys greater than or equal to the node's key.
• Both the left and right subtrees must also be binary search trees.

Given the structure of a binary tree and a sequence of distinct integer keys, there is only one way to fill these keys into the tree so that the resulting tree satisfies the definition of a BST. You are supposed to output the level order traversal sequence of that tree. The sample is illustrated by Figure 1 and 2.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤100) which is the total number of nodes in the tree. The next N lines each contains the left and the right children of a node in the format left_index right_index, provided that the nodes are numbered from 0 to N−1, and 0 is always the root. If one child is missing, then −1 will represent the NULL child pointer. Finally N distinct integer keys are given in the last line.

Output Specification:

For each test case, print in one line the level order traversal sequence of that tree. All the numbers must be separated by a space, with no extra space at the end of the line.

Sample Input:

9
1 6
2 3
-1 -1
-1 4
5 -1
-1 -1
7 -1
-1 8
-1 -1
73 45 11 58 82 25 67 38 42

Sample Output:

58 25 82 11 38 67 45 73 42

经验总结：

emmmm  迄今为止做到最简单的30分的题目了，通过率0.57也足以说明，首先把所给序列从小到大排个序，然后中序遍历树，将此序列依次填入，然后再层序遍历就行啦~

AC代码

#include <cstdio>
#include <queue>
#include <algorithm>
using namespace std;
const int maxn=110;
int pre[maxn],level[maxn],n,pos=0;
struct node
{
	int lchild,rchild,data;
}Node[maxn];
void inorder(int root)
{
	if(root==-1)
		return ;
	if(Node[root].lchild!=-1)
		inorder(Node[root].lchild);
	Node[root].data=pre[pos++];
	if(Node[root].rchild!=-1)
		inorder(Node[root].rchild);
}
void levelorder(int root)
{
	queue<node> q;
	pos=0;
	q.push(Node[root]);
	while(q.size())
	{
		node x=q.front();
		q.pop();
		level[pos++]=x.data;
		if(x.lchild!=-1)
			q.push(Node[x.lchild]);
		if(x.rchild!=-1)
			q.push(Node[x.rchild]);
	}
}
int main()
{
	scanf("%d",&n);
	for(int i=0;i<n;++i)
		scanf("%d%d",&Node[i].lchild,&Node[i].rchild);
	for(int i=0;i<n;++i)
		scanf("%d",&pre[i]);
	sort(pre,pre+n);
	inorder(0);
	levelorder(0);
	for(int i=0;i<n;++i)
		printf("%d%c",level[i],i<n-1?' ':'\n');
	return 0;
}