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题意：输出2到n在一颗不平衡二叉排序树里面的父节点的编号

思路：显然边建树边输出是会TLE的，那么开个set乱搞一下就可以了


#include<iostream>
#include<cstdio>
#include<map>
#include<set>
using namespace std;
const int maxn = 1e5+6;
map<int,int>pos;
set<int> s;

int main()
{
    int n;
	scanf("%d",&n);
	int temp;
	scanf("%d",&temp);
	s.insert(0);
	s.insert(temp);
//	s.insert(1e9+100);
    pos[temp]=1;

	for (int i = 2;i<=n;i++)
	{
        cin >> temp;
		set<int>::iterator it = s.lower_bound(temp);
		set<int>::iterator it1 = it;
		set<int>::iterator it2 = it;
		it1--;
		if (pos[*it1]>pos[*it2])
		     printf("%d\n",*it1);
		else
			printf("%d\n",*it2);
		s.insert(temp);
		pos[temp]=i;
	}
	printf("\n");
}


D. Tree Construction time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output

During the programming classes Vasya was assigned a difficult problem. However, he doesn't know how to code and was unable to find the solution in the Internet, so he asks you to help.

You are given a sequence a, consisting of n distinct integers, that is used to construct the binary search tree. Below is the formal description of the construction process.

  1. First element a1 becomes the root of the tree.
  2. Elements a2, a3, ..., an are added one by one. To add element ai one needs to traverse the tree starting from the root and using the following rules:
    1. The pointer to the current node is set to the root.
    2. If ai is greater than the value in the current node, then its right child becomes the current node. Otherwise, the left child of the current node becomes the new current node.
    3. If at some point there is no required child, the new node is created, it is assigned value ai and becomes the corresponding child of the current node.
Input

The first line of the input contains a single integer n (2 ≤ n ≤ 100 000) — the length of the sequence a.

The second line contains n distinct integers ai (1 ≤ ai ≤ 109) — the sequence a itself.

Output

Output n - 1 integers. For all i > 1 print the value written in the node that is the parent of the node with value ai in it.

Examples input 
3
1 2 3
output 
1 2
input 
5
4 2 3 1 6
output 
4 2 2 4
Note

Picture below represents the tree obtained in the first sample.

Picture below represents the tree obtained in the second sample.


本文标签： codeforcestreesetconstruction

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