Problem:
Score : 800 points

Problem Statement

Let N be a positive even number.

We have a permutation of (1, 2, ..., N), p = (p_1, p_2, ..., p_N).
Snuke is constructing another permutation of (1, 2, ..., N), q, following the procedure below.

First, let q be an empty sequence.
Then, perform the following operation until p becomes empty:

Select two adjacent elements in p, and call them x and y in order. Remove x and y from p (reducing the length of p by 2), and insert x and y, preserving the original order, at the beginning of q.

When p becomes empty, q will be a permutation of (1, 2, ..., N).

Find the lexicographically smallest permutation that can be obtained as q.

Constraints

N is an even number.

2 ≤ N ≤ 2 × 10^5

p is a permutation of (1, 2, ..., N).

Input

Input is given from Standard Input in the following format:

N
p_1 p_2 ... p_N

Output

Print the lexicographically smallest permutation, with spaces in between.

Sample Input 1

4
3 2 4 1

Sample Output 1

3 1 2 4

The solution above is obtained as follows:

p

q

(3, 2, 4, 1)

()

↓

↓

(3, 1)

(2, 4)

↓

↓

()

(3, 1, 2, 4)

Sample Input 2

2
1 2

Sample Output 2

1 2

Sample Input 3

8
4 6 3 2 8 5 7 1

Sample Output 3

3 1 2 7 4 6 8 5

The solution above is obtained as follows:

p

q

(4, 6, 3, 2, 8, 5, 7, 1)

()

↓

↓

(4, 6, 3, 2, 7, 1)

(8, 5)

↓

↓

(3, 2, 7, 1)

(4, 6, 8, 5)

↓

↓

(3, 1)

(2, 7, 4, 6, 8, 5)

↓

↓

()

(3, 1, 2, 7, 4, 6, 8, 5)

Solution in Rust (1.42.0) (judge verdict: Accepted)

//---------- begin SegmentTree Point update Range query ----------
pub trait PURQ {
    type T: Clone;
    fn fold(l: &Self::T, r: &Self::T) -> Self::T;
    fn e() -> Self::T;
}

struct SegmentTreePURQ<R: PURQ> {
    seg: Vec<R::T>,
    size: usize,
}

#[allow(dead_code)]
impl<R: PURQ> SegmentTreePURQ<R> {
    fn new(n: usize) -> SegmentTreePURQ<R> {
        let size = n.next_power_of_two();
        SegmentTreePURQ {
            seg: vec![R::e(); 2 * size],
            size: size,
        }
    }
    fn build_by(a: &[R::T]) -> SegmentTreePURQ<R> {
        let size = a.len().next_power_of_two();
        let mut b = vec![R::e(); 2 * size];
        for i in 0..a.len() {
            b[i + size] = a[i].clone();
        }
        let mut seg = SegmentTreePURQ {
            seg: b,
            size: size,
        };
        seg.update_all();
        seg
    }
    fn update(&mut self, x: usize, v: R::T) {
        let mut x = x + self.size;
        let a = &mut self.seg;
        a[x] = v;
        x >>= 1;
        while x > 0 {
            a[x] = R::fold(&a[2 * x], &a[2 * x + 1]);
            x >>= 1;
        }
    }
    fn update_tmp(&mut self, x: usize, v: R::T) {
        self.seg[self.size + x] = v;
    }
    fn update_all(&mut self) {
        let a = &mut self.seg;
        for i in (1..self.size).rev() {
            a[i] = R::fold(&a[2 * i], &a[2 * i + 1]);
        }
    }
    fn find(&self, l: usize, r: usize) -> R::T {
        let mut x = R::e();
        let mut y = R::e();
        let mut l = l + self.size;
        let mut r = r + self.size;
        let a = &self.seg;
        while l < r {
            if l & 1 == 1 {
                x = R::fold(&x, &a[l]);
                l += 1;
            }
            if r & 1 == 1 {
                r -= 1;
                y = R::fold(&a[r], &y);
            }
            l >>= 1;
            r >>= 1;
        }
        R::fold(&x, &y)
    }
}
//---------- end SegmentTree Point update Range query ----------

use proconio::*;
use std::cmp::*;

struct RMQ;
impl PURQ for RMQ {
    type T = (u32, usize);
    fn fold(l: &Self::T, r: &Self::T) -> Self::T {
        std::cmp::min(*l, *r)
    }
    fn e() -> Self::T {
        (std::u32::MAX, std::usize::MAX)
    }
}

#[fastout]
fn run() {
    input! {
        n: usize,
        p: [u32; n],
    }
    let mut seg = (0..2).map(|_| SegmentTreePURQ::<RMQ>::new(n)).collect::<Vec<_>>();
    for (i, p) in p.iter().enumerate() {
        seg[i & 1].update_tmp(i, (*p, i));
    }
    seg.iter_mut().for_each(|s| s.update_all());
    let find = |l: usize, r: usize| -> (u32, u32, usize, usize, usize, usize) {
        assert!(l + 2 <= r);
        let (a, x) = seg[l & 1].find(l, r);
        let (b, y) = seg[(l & 1) ^ 1].find(x, r);
        (a, b, l, r, x, y)
    };
    let mut h = std::collections::BinaryHeap::new();
    h.push(Reverse(find(0, n)));
    let mut ans = vec![];
    while let Some(Reverse((a, b, l, r, x, y))) = h.pop() {
        ans.push(a);
        ans.push(b);
        for &(l, r) in [(l, x), (x + 1, y), (y + 1, r)].iter() {
            if l + 2 <= r {
                h.push(Reverse(find(l, r)));
            }
        }
    }
    let mut s = String::new();
    for a in ans {
        s.push_str(&format!("{} ", a));
    }
    s.pop();
    println!("{}", s);
}

fn main() {
    run();
}