Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của flashmt

uses math;
var l,r:array[0..100000] of longint;
    n,i,x,m:longint;

begin
        read(n);
        for i:=1 to n do r[i]:=i+1;
        for i:=2 to n do l[i]:=i-1;
        m:=0;
        for i:=1 to n do
        begin
                read(x);
                if r[x]<m then
                begin
                        writeln('YES');
                        halt;
                end;
                r[l[x]]:=r[x];
                l[r[x]]:=l[x];
                m:=max(m,x);
        end;
        writeln('NO');
end.

Code mẫu của happyboy99x

#include <algorithm>
#include <bitset>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;

typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<vii> vvii;
typedef vector<int> vi;
typedef vector<vi> vvi;

#define sz(a) int((a).size())
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define all(c) (c).begin(), (c).end()
#define tr(c,i) for(typeof((c).begin()) i = (c).begin(), _e = (c).end(); i != _e; ++i)
#define present(c,x) ((c).find(x) != (c).end())
#define cpresent(c,x) (find(all(c),x) != (c).end())
#define rep(i,n) for(int i = 0, _n = (n); i < _n; ++i)
#define repd(i,n) for(int i = (n)-1; i >= 0; --i )
#define fo(i,a,b) for(int i = (a), _b = (b); i <= _b; ++i)
#define fod(i,a,b) for(int i = (a), _b = (b); i >= _b; --i)

#define INF 1000000000
#define N 100000

int prev[N+2], next[N+2], n;

int main() {
    scanf("%d",&n);
    fo(i,1,n) { prev[i] = i+1; next[i] = i-1; }
    int last = 0;
    rep(i,n) {
        int v; scanf("%d",&v);
        if( v != next[last] && v < last ) { puts("YES"); return 0; }
        next[prev[v]] = next[v];
        prev[next[v]] = prev[v];
        last = v;
    }
    puts("NO");
    return 0;
}

Code mẫu của RR

var
  a,s:array[1..1000111] of longint;
  u,i,top,n:longint;
begin
  read(n);
  for i:=1 to n do read(a[i]);
  top:=0; u:=1;
  for i:=1 to n do
    begin
      inc(top); s[top]:=i;
      while (a[u]=s[top]) do
        begin
          inc(u);
          dec(top);
        end;
    end;

  while (top>0) and (a[u]=s[top]) do
    begin
      dec(top);
      inc(u);
    end;

  if top>0 then writeln('YES')
  else writeln('NO');
end.

Code mẫu của hieult

#include <stdio.h>
//#include <conio.h>
main()
{
long n;
int vaolo[100001],a[100001],t=0;
//FILE *p;
//p=fopen("D:\\Hoc tap\\test\\CHeat\\CHEAT.IN4","r");
scanf("%ld",&n);
for(long i=1;i<=n;i++)
  {
  scanf("%d",&a[i]);
  vaolo[i]=0;
  }
vaolo[a[1]]=1;
for(long i=2;i<=n;i++)
  {
  vaolo[a[i]]=1;
  if(a[i]<a[i-1])
    {
    for(long j=a[i]+1;j<=a[i-1]-1;j++)
      if(vaolo[j]==0)
        {
        printf("YES");
        t=1;
        break;
        }
    if(t==1)
      break;    
    }
  }  
if(t==0)
  printf("NO");
//getch();
}

Code mẫu của ll931110

program CHEAT; 
const 
        fi=''; 
        fo=''; 
var 
        f:text; 
        free:array[1..100000] of boolean; 
        i,j,n,h,k:longint; 
        angian:boolean; 
procedure xuly; 
begin 
        assign(f,fi); 
        reset(f); 
        readln(f,n); 
        fillchar(free,n,true); 
        angian:=false; 
        for i:= 1 to n do 
                begin 
                readln(f,k); 
                free[k]:=false; 
                if h>k then 
                for j:= k to h do 
                       if free[j] then 
                       begin 
                       angian:=true; 
                       exit; 
                       end; 
                h:=k; 
                end; 
        close(f); 
end; 
procedure xuat; 
begin 
        assign(f,fo); 
        rewrite(f); 
        if angian=true then write(f,'YES') 
        else 
        write(f,'NO'); 
        close(f); 
end; 
begin {main} 
xuly; 
xuat; 
end.

Code mẫu của khuc_tuan

const
    maxn = 100000;

var
    bit, vt, a : array[1..maxn] of longint;
    x, k, t, p, i, j, n : longint;
    f : array[0..16,1..maxn] of longint;

procedure add(i, v : longint);
begin
    while i<=n do begin
        inc(bit[i],v);
        inc(i,i and (-i));
    end;
end;

function tinh(i : longint) : longint;
var res : longint;
begin
    res := 0;
    while i>0 do begin
        inc(res,bit[i]);
        i := i and (i-1);
    end;
    tinh := res;
end;

function find(i : longint) : longint;
var
    l, r, m, a : longint;
begin
    a := tinh(i);
    l := 1;
    r := i;
    while l<r do begin
        m := (l+r) div 2;
        if tinh(m)=a then r := m
        else l := m+1;
    end;
    find := l;
end;

begin
    read(n);
    for i:=1 to n do begin
        read(a[i]);
        vt[a[i]] := i;
        f[0,i] := a[i];
    end;
    p := 1;
    for i:=1 to 16 do begin
        for j:=1 to n-p+1 do begin
            f[i,j] := f[i-1,j+p];
            if f[i,j]>f[i-1,j] then f[i,j] := f[i-1,j];
        end;
        p := 2*p;
    end;
    for i:=n downto 1 do begin
        if (i<=n-2) and (tinh(a[i])>0) then begin
            j := vt[find(a[i])];
            t := trunc(ln(j-i+1)/ln(2) + 1e-9);
            p := 1;
            for x:=1 to t do p:=2*p;
            k := f[t,j-p+1];
            if k>f[t,i] then k := f[t,i];
            if k<a[j] then begin
                writeln('YES');
                exit;
            end;
        end;
        add(a[i],1);
    end;
    writeln('NO');
end.