原题干：
A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:
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The left subtree of a node contains only nodes with keys less than the node's key.
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The right subtree of a node contains only nodes with keys greater than or equal to the node's key.
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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
题目大意：
第一行给出二叉树节点数量N，往后的几行给出从0-(N-1)的节点左右孩子编号，NULL以-1表示。最后一行给出要插入的序列。
将序列插入二叉树中，使之称为二叉搜索树，输出二叉搜索树的前序遍历结果。
对于这样将序列插入二叉搜索树的问题，我们通常的解决办法是将序列进行排序，因为二叉搜索树的中序遍历序列是有序的，所以排序后正是二叉搜索树的中序遍历序列。
接着我们使用中序插入的方式插入二叉树。
至于什么是中序插入？其实就是中序遍历的输出代码换做插入代码即可。这样就成功插入到了二叉搜索树中。
接着我们使用BFS算法进行层序遍历，得出结果。
代码如下：
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;
typedef struct{
int data;
int lchild, rchild;
} node;
/*全局变量*/
int cnt;
node tree[110];
int input[110];
int num = 0;
/*中序递归插入*/
void insert(int root){
if(root == -1) return;
insert(tree[root].lchild);
tree[root].data = input[num++];
insert(tree[root].rchild);
}
void BFS(int root){
queue<int> Q;
Q.push(root);
int sum = 0;
while(!Q.empty()){
int top = Q.front();
Q.pop();
cout << tree[top].data;
if(++sum < cnt) cout << " ";
if(tree[top].lchild != -1)
Q.push(tree[top].lchild);
if(tree[top].rchild != -1)
Q.push(tree[top].rchild);
}
}
int main(){
cin >> cnt;
for(int i = 0; i < cnt; i++) //读入树的模型
cin >> tree[i].lchild >> tree[i].rchild;
for(int i = 0; i < cnt; i++) //读入序列
cin >> input[i];
sort(input, input + cnt); //变成中序遍历序列
insert(0);
BFS(0);
return 0;
}