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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.IO;
using System.Text;
using System.Diagnostics;

using Binary = System.Func<System.Linq.Expressions.ParameterExpression, System.Linq.Expressions.ParameterExpression, System.Linq.Expressions.BinaryExpression>;
using Unary = System.Func<System.Linq.Expressions.ParameterExpression, System.Linq.Expressions.UnaryExpression>;

class Program
{
    static StreamWriter sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
    static Scan sc = new Scan();
    const int M = 1000000007;
    const double eps = 1e-11;
    static readonly int[] dd = { 0, 1, 0, -1, 0 };
    static void Main()
    {
        int n = sc.Int;
        var p = sc.IntArr;
        var odmin = new Segtree<Tuple<int, int>>(n, (i, j) => i.Item1 < j.Item1 ? i : j, new Tuple<int, int>(M, -1));
        var evmin = new Segtree<Tuple<int, int>>(n, (i, j) => i.Item1 < j.Item1 ? i : j, new Tuple<int, int>(M, -1));
        for (int i = 0; i < n / 2; i++)
        {
            evmin.assign(i * 2, new Tuple<int, int>(p[i * 2], i * 2));
            odmin.assign(i * 2 + 1, new Tuple<int, int>(p[i * 2 + 1], i * 2 + 1));
        }
        evmin.all_update();
        odmin.all_update();
        var q = new PriorityQueue<range>();
        q.Push(new range(0, n, evmin.run(0, n).Item1));
        var ans = new List<int>();
        while (q.Count > 0)
        {
            var a = q.Pop();
            int l = a.l, r = a.r;
            if (r - l < 2) continue;
            if (l % 2 == 0) {
                var ti = evmin.run(l, r);
                var tj = odmin.run(ti.Item2, r);
                ans.Add(ti.Item1);
                ans.Add(tj.Item1);
                q.Push(new range(l, ti.Item2, evmin.run(l, ti.Item2).Item1));
                q.Push(new range(ti.Item2 + 1, tj.Item2, odmin.run(ti.Item2, tj.Item2).Item1));
                q.Push(new range(tj.Item2 + 1, r, evmin.run(tj.Item2, r).Item1));
            }
            else {
                var ti = odmin.run(l, r);
                var tj = evmin.run(ti.Item2, r);
                ans.Add(ti.Item1);
                ans.Add(tj.Item1);
                q.Push(new range(l, ti.Item2, odmin.run(l, ti.Item2).Item1));
                q.Push(new range(ti.Item2 + 1, tj.Item2, evmin.run(ti.Item2, tj.Item2).Item1));
                q.Push(new range(tj.Item2 + 1, r, odmin.run(tj.Item2, r).Item1));
            }
        }
        Prt(ans);
        sw.Flush();
    }
    class range : IComparable<range>
    {
        public int l, r, priority;
        public range(int l, int r, int p) {
            this.l = l;
            this.r = r;
            this.priority = p;
        }
        public int CompareTo(range a) {
            return a.priority.CompareTo(priority);
        }
    }


    static void swap<T>(ref T a, ref T b) { var t = a; a = b; b = t; }
    static T Max<T>(params T[] a) { return a.Max(); }
    static T Min<T>(params T[] a) { return a.Min(); }
    static void DBG(string a) { Console.WriteLine(a); }
    static void Prt(string a) { sw.WriteLine(a); }
    static void DBG<T>(IEnumerable<T> a) { DBG(string.Join(" ", a)); }
    static void DBG(params object[] a) { DBG(string.Join(" ", a)); }
    static void Prt<T>(IEnumerable<T> a) { Prt(string.Join(" ", a)); }
    static void Prt(params object[] a) { Prt(string.Join(" ", a)); }

    // for AOJ
    // static string Join<T>(string sep, IEnumerable<T> a) { return string.Join(sep, a.Select(x => x.ToString()).ToArray()); }
    // static void DBG<T>(IEnumerable<T> a) { DBG(Join(" ", a)); }
    // static void DBG(params object[] a) { DBG(Join(" ", a)); }
    // static void Prt<T>(IEnumerable<T> a) { Prt(Join(" ", a)); }
    // static void Prt(params object[] a) { Prt(Join(" ", a)); }
}
static class ex
{
    public static void swap<T>(this IList<T> a, int i, int j) { var t = a[i]; a[i] = a[j]; a[j] = t; }
    public static T[] copy<T>(this IList<T> a)
    {
        var ret = new T[a.Count];
        for (int i = 0; i < a.Count; i++) ret[i] = a[i];
        return ret;
    }
}
static class Operator<T>
{
    static readonly ParameterExpression x = Expression.Parameter(typeof(T), "x");
    static readonly ParameterExpression y = Expression.Parameter(typeof(T), "y");
    public static readonly Func<T, T, T> Add = Lambda(Expression.Add);
    public static readonly Func<T, T, T> Subtract = Lambda(Expression.Subtract);
    public static readonly Func<T, T, T> Multiply = Lambda(Expression.Multiply);
    public static readonly Func<T, T, T> Divide = Lambda(Expression.Divide);
    public static readonly Func<T, T> Plus = Lambda(Expression.UnaryPlus);
    public static readonly Func<T, T> Negate = Lambda(Expression.Negate);
    public static Func<T, T, T> Lambda(Binary op) { return Expression.Lambda<Func<T, T, T>>(op(x, y), x, y).Compile(); }
    public static Func<T, T> Lambda(Unary op) { return Expression.Lambda<Func<T, T>>(op(x), x).Compile(); }
}

class Scan
{
    public int Int { get { return int.Parse(Str); } }
    public long Long { get { return long.Parse(Str); } }
    public double Double { get { return double.Parse(Str); } }
    public string Str { get { return Console.ReadLine().Trim(); } }
    public int[] IntArr { get { return StrArr.Select(int.Parse).ToArray(); } }
    public long[] LongArr { get { return StrArr.Select(long.Parse).ToArray(); } }
    public double[] DoubleArr { get { return StrArr.Select(double.Parse).ToArray(); } }
    public string[] StrArr { get { return Str.Split(); } }
    bool eq<T, U>() { return typeof(T).Equals(typeof(U)); }
    T ct<T, U>(U a) { return (T)Convert.ChangeType(a, typeof(T)); }
    T cv<T>(string s) { return eq<T, int>()    ? ct<T, int>(int.Parse(s))
                             : eq<T, long>()   ? ct<T, long>(long.Parse(s))
                             : eq<T, double>() ? ct<T, double>(double.Parse(s))
                             : eq<T, char>()   ? ct<T, char>(s[0])
                                               : ct<T, string>(s); }
    public void Multi<T>(out T a) { a = cv<T>(Str); }
    public void Multi<T, U>(out T a, out U b)
    { var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]); }
    public void Multi<T, U, V>(out T a, out U b, out V c)
    { var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); }
    public void Multi<T, U, V, W>(out T a, out U b, out V c, out W d)
    { var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]); }
    public void Multi<T, U, V, W, X>(out T a, out U b, out V c, out W d, out X e)
    { var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]); e = cv<X>(ar[4]); }
    public void Multi<T, U, V, W, X, Y>(out T a, out U b, out V c, out W d, out X e, out Y f)
    { var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]); e = cv<X>(ar[4]); f = cv<Y>(ar[5]); }
    public void Multi<T, U, V, W, X, Y, Z>(out T a, out U b, out V c, out W d, out X e, out Y f, out Z g)
    { var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]); e = cv<X>(ar[4]); f = cv<Y>(ar[5]);  g = cv<Z>(ar[6]);}
}
class mymath
{
    public static long Mod = 1000000007;
    public static bool isprime(long a)
    {
        if (a < 2) return false;
        for (long i = 2; i * i <= a; i++) if (a % i == 0) return false;
        return true;
    }
    public static bool[] sieve(int n)
    {
        var p = new bool[n + 1];
        for (int i = 2; i <= n; i++) p[i] = true;
        for (int i = 2; i * i <= n; i++) if (p[i]) for (int j = i * i; j <= n; j += i) p[j] = false;
        return p;
    }
    public static List<int> getprimes(int n)
    {
        var prs = new List<int>();
        var p = sieve(n);
        for (int i = 2; i <= n; i++) if (p[i]) prs.Add(i);
        return prs;
    }
    public static long[][] E(int n)
    {
        var ret = new long[n][];
        for (int i = 0; i < n; i++) { ret[i] = new long[n]; ret[i][i] = 1; }
        return ret;
    }
    public static double[][] dE(int n)
    {
        var ret = new double[n][];
        for (int i = 0; i < n; i++) { ret[i] = new double[n]; ret[i][i] = 1; }
        return ret;
    }
    public static long[][] pow(long[][] A, long n)
    {
        if (n == 0) return E(A.Length);
        var t = pow(A, n / 2);
        if ((n & 1) == 0) return mul(t, t);
        return mul(mul(t, t), A);
    }
    public static double[][] pow(double[][] A, long n)
    {
        if (n == 0) return dE(A.Length);
        var t = pow(A, n / 2);
        if ((n & 1) == 0) return mul(t, t);
        return mul(mul(t, t), A);
    }
    public static double dot(double[] x, double[] y)
    {
        int n = x.Length;
        double ret = 0;
        for (int i = 0; i < n; i++) ret += x[i] * y[i];
        return ret;
    }
    public static double _dot(double[] x, double[] y)
    {
        int n = x.Length;
        double ret = 0, r = 0;
        for (int i = 0; i < n; i++)
        {
            double s = ret + (x[i] * y[i] + r);
            r = (x[i] * y[i] + r) - (s - ret);
            ret = s;
        }
        return ret;
    }
    public static long dot(long[] x, long[] y)
    {
        int n = x.Length;
        long ret = 0;
        for (int i = 0; i < n; i++) ret = (ret + x[i] * y[i]) % Mod;
        return ret;
    }
    public static T[][] trans<T>(T[][] A)
    {
        int n = A[0].Length, m = A.Length;
        var ret = new T[n][];
        for (int i = 0; i < n; i++) { ret[i] = new T[m]; for (int j = 0; j < m; j++) ret[i][j] = A[j][i]; }
        return ret;
    }
    public static double[] mul(double[][] A, double[] x)
    {
        int n = A.Length;
        var ret = new double[n];
        for (int i = 0; i < n; i++) ret[i] = dot(x, A[i]);
        return ret;
    }
    public static long[] mul(long[][] A, long[] x)
    {
        int n = A.Length;
        var ret = new long[n];
        for (int i = 0; i < n; i++) ret[i] = dot(x, A[i]);
        return ret;
    }
    public static long[][] mul(long[][] A, long[][] B)
    {
        int n = A.Length;
        var Bt = trans(B);
        var ret = new long[n][];
        for (int i = 0; i < n; i++) ret[i] = mul(Bt, A[i]);
        return ret;
    }
    public static double[][] mul(double[][] A, double[][] B)
    {
        int n = A.Length;
        var Bt = trans(B);
        var ret = new double[n][];
        for (int i = 0; i < n; i++) ret[i] = mul(Bt, A[i]);
        return ret;
    }
    public static long[] add(long[] x, long[] y)
    {
        int n = x.Length;
        var ret = new long[n];
        for (int i = 0; i < n; i++) ret[i] = (x[i] + y[i]) % Mod;
        return ret;
    }
    public static long[][] add(long[][] A, long[][] B)
    {
        int n = A.Length;
        var ret = new long[n][];
        for (int i = 0; i < n; i++) ret[i] = add(A[i], B[i]);
        return ret;
    }
    public static long pow(long a, long b)
    {
        if (a >= Mod) return pow(a % Mod, b);
        if (a == 0) return 0;
        if (b == 0) return 1;
        var t = pow(a, b / 2);
        if ((b & 1) == 0) return t * t % Mod;
        return t * t % Mod * a % Mod;
    }
    public static long inv(long a) { return pow(a, Mod - 2); }
    public static long gcd(long a, long b)
    {
        while (b > 0) { var t = a % b; a = b; b = t; }
        return a;
    }
    // a x + b y = gcd(a, b)
    public static long extgcd(long a, long b, out long x, out long y)
    {
        long g = a; x = 1; y = 0;
        if (b > 0) { g = extgcd(b, a % b, out y, out x); y -= a / b * x; }
        return g;
    }
    public static long lcm(long a, long b) { return a / gcd(a, b) * b; }
    public static long comb(int n, int r)
    {
        if (n < 0 || r < 0 || r > n) return 0;
        if (n - r < r) r = n - r;
        if (r == 0) return 1;
        if (r == 1) return n;
        int[] numer = new int[r], denom = new int[r];
        for (int k = 0; k < r; k++) { numer[k] = n - r + k + 1; denom[k] = k + 1; }
        for (int p = 2; p <= r; p++)
        {
            int piv = denom[p - 1];
            if (piv > 1)
            {
                int ofst = (n - r) % p;
                for (int k = p - 1; k < r; k += p) { numer[k - ofst] /= piv; denom[k] /= piv; }
            }
        }
        long ret = 1;
        for (int k = 0; k < r; k++) if (numer[k] > 1) ret = ret * numer[k] % Mod;
        return ret;
    }
}

class Segtree<T>
{
    int n, s, t;
    T[] tr;
    Func<T, T, T> f;
    T exnum;

    // expect : f(ex, ex) = ex
    public Segtree(int m, Func<T, T, T> f, T ex)
    {
        this.f = f; this.exnum = ex; n = 1;
        while (n < m) n <<= 1;
        tr = new T[(n << 1) - 1];
        for (int i = 0; i < tr.Length; i++) tr[i] = ex;
    }
    public Segtree(int m, T ini, Func<T, T, T> f, T ex) : this(m, f, ex)
    {
        for (int i = 0; i < m; ++i) tr[i + n - 1] = ini;
        all_update();
    }
    public void assign(int j, T x) => tr[j + n - 1] = x;
    public void update(int j, T x)
    {
        int i = j + n - 1;
        tr[i] = x;
        while (i > 0) { i = i - 1 >> 1; tr[i] = f(tr[i << 1 | 1], tr[i + 1 << 1]); }
    }
    public void all_update() { for (int i = n - 2; i >= 0; i--) tr[i] = f(tr[i << 1 | 1], tr[i + 1 << 1]); }
    public T look(int i) => tr[i + n - 1];

    // [s, t)
    public T run(int s, int t) { this.s = s; this.t = t; return q(0, 0, n); }
    T q(int k, int l, int r) => r <= s || t <= l ? exnum : s <= l && r <= t ? tr[k]
                              : f(q(k << 1 | 1, l, l + r >> 1), q(k + 1 << 1, l + r >> 1, r));
}

// the greatest element pops
class PriorityQueue<T> where T : IComparable<T>
{
    List<T> buf;
    public bool rev = false;
    public PriorityQueue() { buf = new List<T>(); }
    int cmp(int i, int j) { return buf[i].CompareTo(buf[j]) * (rev ? -1 : 1); }
    void swap(int i, int j) { var t = buf[i]; buf[i] = buf[j]; buf[j] = t; }
    public void Push(T elem)
    {
        int n = buf.Count;
        buf.Add(elem);
        while (n > 0)
        {
            int i = (n - 1) >> 1;
            if (cmp(n, i) > 0) swap(i, n);
            n = i;
        }
    }
    public T Pop()
    {
        T ret = buf[0];
        int n = buf.Count - 1;
        buf[0] = buf[n];
        buf.RemoveAt(n);
        for (int i = 0, j; (j = (i << 1) + 1) < n; i = j)
        {
            if (j != n - 1 && cmp(j, j + 1) < 0) ++j;
            if (cmp(i, j) < 0) swap(i, j);
        }
        return ret;
    }
    public T Top { get { return buf[0]; } }
    public int Count { get { return buf.Count; } }
}