1099. Build A Binary Search Tree

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:

91 62 3-1 -1-1 45 -1-1 -17 -1-1 8-1 -173 45 11 58 82 25 67 38 42

Sample Output:

58 25 82 11 38 67 45 73 42

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <deque>
#include <queue>
#include <cstring>
#include <vector>
#include <string>
#include <iomanip>
#include <map>
#include <set>
#include <cmath>
#include <stack>
#include <cmath>
#include <algorithm>
using namespace std;
#define max1 100001
#define inf -1
typedef struct Node
{
int data;
int Lchild;
int Rchild;
int lNum;
int rNum;
int val;
};
int n,b[101];
vector<Node>tree;
int count1(int cur)
{
if(cur==-1)return 0;
tree[cur].lNum=count1(tree[cur].Lchild);
tree[cur].rNum=count1(tree[cur].Rchild);
return tree[cur].lNum+tree[cur].rNum+1;
}
void build(int cur,int l,int r)
{
if(cur==-1)return;
int idx=l+tree[cur].lNum;
tree[cur].val=b[idx];
build(tree[cur].Lchild,l,idx);
build(tree[cur].Rchild,idx+1,r);
}
void levelOrder()
{
queue<int> que;
que.push(0);
int flag=0;
while(!que.empty())
{
int temp=que.front();
que.pop();
if(!flag)
{
cout<<tree[temp].val;
flag=1;
}
else
{
cout<<' '<<tree[temp].val;
}
if(tree[temp].Lchild!=-1)que.push(tree[temp].Lchild);
if(tree[temp].Rchild!=-1)que.push(tree[temp].Rchild);
}
}
int main()
{
   cin>>n;
   int i;
   tree.resize(n);
   for(i=0;i<n;i++)
   {
    cin>>tree[i].Lchild>>tree[i].Rchild;
   }
   for(i=0;i<n;i++)
   {
    cin>>b[i];
   }
   sort(b,b+n);
   count1(0);
   build(0,0,n);
   levelOrder();
   return 0;
}