1099. Build A Binary Search Tree (30)

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. 

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.

IDEA

1.二叉排序树的中序遍历（左根右）序列的值是从小到大排列的

2.用到 

#ifndef ONLINE_JUDGE
freopen("input.txt","r",stdin);
#endif

#ifndef ONLINE_JUDGE
fclose(stdin);
#endif

3.先进行中序遍历，根据该节点值在全节点中的大小位置，映射到data数组中，确定其值

4.然后进行层序遍历（用queue），输出值



CODE

//二叉排序树的中序遍历（左根右）序列的值是从小到大的序列
#include<iostream>
#include<vector>
#include<queue>
#include<algorithm>
#include<fstream>
using namespace std;
#define MAX 101
struct Node{
int data;
int left,right;
};
Node tree[MAX];
int data[MAX];
void InOrder(int root){
static int index=0;
if(root==-1){
return;
}
InOrder(tree[root].left);//左
tree[root].data=data[index++];//根
//cout<<tree[root].data<<"_";
InOrder(tree[root].right);//右
}
void LevelOrder(int root,vector<int> &seq){
queue<int> que;
que.push(root);
while(!que.empty()){
int tmp=que.front();
que.pop();
seq.push_back(tree[tmp].data);
if(tree[tmp].left!=-1){
que.push(tree[tmp].left);
}
if(tree[tmp].right!=-1){
que.push(tree[tmp].right);
}
}
}
int main(){
#ifndef ONLINE_JUDGE
freopen("input.txt","r",stdin);
#endif

int n;
cin>>n;
for(int i=0;i<n;i++){
cin>>tree[i].left>>tree[i].right;
//cout<<tree[i].left<<" "<<tree[i].right<<endl;
}

for(int i=0;i<n;i++){
cin>>data[i];
}
sort(data,data+n);//从小到大排序

int root=0;
InOrder(root);//中序遍历二叉排序数，确定节点数值的从小到大的顺序

vector<int> result;
LevelOrder(root,result);

vector<int>::iterator it;
for(it=result.begin();it!=result.end();it++){
//cout<<*it<<"_";
if(it==result.begin()){
cout<<*it;
}else{
cout<<" "<<*it;
}
}
#ifndef ONLINE_JUDGE
fclose(stdin);
#endif
return 0;
}