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

#include <iostream>
#include <algorithm>
using namespace std;

int n,k,re,a[100100],d[100100],mx[100100];

int ok(int maxVal)
{
 long long biggest=0;
 for (int i=1;i<=maxVal;i++)
 {
  if (biggest+1<i) return 0;
  if (d[i])
  {
    biggest+=1LL*i*d[i];
    if (biggest>=k) return 1;
  }
 }
 return 0;
}

int main()
{
 int test;
 cin >> test;
 while (test--)
 {
  re=mx[0]=-1;
  cin >> n >> k;
  for (int i=1;i<=n;i++) scanf("%d",&a[i]), mx[i]=max(mx[i-1],a[i]);
  int l=1,r=n,m,last=0;
  while (l<=r)
  {
   m=(l+r)/2;
   if (m<last) 
    for (int i=m+1;i<=last;i++) d[a[i]]--;
   else
    for (int i=last+1;i<=m;i++) d[a[i]]++;
   if (ok(mx[m])) re=m, r=m-1;
   else l=m+1;
   last=m;
  }
  cout << re << endl; 
  for (int i=1;i<=m;i++) d[a[i]]--;
 }
}

Code mẫu của ladpro98

program riddle;
uses    math;
const   maxn=trunc(1e5)+5;
        fi='';
var     a,org:array[1..maxn] of longint;
        l,r,i,tt,t,n,m,res,k:longint;
        inp:text;

procedure sort(l,r:longint);
var     i,j,p,t:longint;
begin
        if l>=r then exit;
        i:=l;j:=r;
        p:=a[random(r-l+1)+l];
        repeat
                while a[i]<p do inc(i);
                while a[j]>p do dec(j);
                if i<=j then begin
                        if i<j then begin
                                t:=a[i];a[i]:=a[j];a[j]:=t;
                        end;
                        inc(i);dec(j);
                end;
        until i>j;
        sort(l,j);sort(i,r);
end;

function ok(p:longint):boolean;
var     t,i:longint;
begin
        for i:=1 to p do a[i]:=org[i];
        sort(1,p);t:=0;
        for i:=1 to p do begin
                if a[i]<=t+1 then inc(t,a[i])
                else break;
                if t>=k then exit(true);
        end;
        if t<k then exit(false);
end;

begin
        assign(inp,fi);reset(inp);
        readln(inp,t);
        for tt:=1 to t do begin
                readln(inp,n,k);
                for i:=1 to n do read(inp,org[i]);
                l:=1;r:=n;res:=-1;
                while l<=r do begin
                        m:=(l+r) shr 1;
                        if ok(m) then begin
                                res:=m;
                                r:=m-1;
                        end
                        else    l:=m+1;
                end;
                writeln(res);
        end;
end.

Code mẫu của RR

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <iomanip>
#include <bitset>
#include <complex>

#define FOR(i,a,b) for(int i = a; i <= b; ++i)
#define FORD(i,a,b) for(int i = a; i >= b; --i)
#define REP(i,a) for(int i = 0; i < a; ++i)
#define MP make_pair
#define PB push_back

using namespace std;

int cnt[100111], a[100111];

int main() {
    int ntest; scanf("%d", &ntest);
    while (ntest--) {
        int n, k; scanf("%d%d", &n, &k);
        int can = 0;
        FOR(i,1,n) scanf("%d", &a[i]);

        memset(cnt, 0, sizeof cnt);
        bool ok = false;
        FOR(i,1,n) {
            if (a[i] > can + 1) {
                ++cnt[a[i]];
                continue;
            }
            int save = can;
            can += a[i];
            for(int x = save + 1; x <= can + 1 && x <= 100001; ++x)
                can += cnt[x] * x;

            if (can >= k) {
                ok = true;
                printf("%d\n", i);
                break;
            }
        }
        if (!ok) puts("-1");
    }
    return 0;
}

Code mẫu của hieult

#include<cstdio>
#include<cmath>
#include<cstring>
#include<cstdlib>
#include<cassert>
#include<ctime>
#include<algorithm>
#include<iterator>
#include<iostream>
#include<cctype>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<list>
//#include<conio.h>
#define ep 0.000000001
#define maxn 10011
#define oo 1111111
#define base 100000000
#define TR(c, it) for(typeof((c).begin()) it=(c).begin(); it!=(c).end(); it++)
#define chia 21266327
double const PI=4*atan(1);

using namespace std;

typedef pair<int, int> II;
typedef vector<int> VI;
typedef vector<II> VII;
typedef vector<VI> VVI;
typedef vector<VII> VVII;

int n,k,a[100111],test,sl[100111],b[100111],run;
long long tong;
bool check;

int tinh(int x){
      memset(sl,0,sizeof(sl));
      for(int i = 0;i<=x;i++) sl[a[i]]++;
      run = 0;
      for(int i = 0;i<=100000;i++){
           for(int j = 0;j<sl[i];j++)
                 b[run++] = i; 
      }
      tong = 0; check = true;
      for(int i = 0;i<=x;i++){
            if(b[i]>tong+1){
                 check = false;
                 break;
            }
            else tong = tong+b[i];
      }
      if(tong>=k && check) return true;
      else return false;
}

int main(){
    // freopen("RIDDLE.in","r",stdin);
     scanf("%d",&test);
     for(int itest = 1;itest<=test;itest++){
          scanf("%d %d",&n,&k);
          for(int i = 0;i<n;i++) scanf("%d",&a[i]);
          int u = 0, v = n , r;
          while(u<v){
               r = (u+v)/2;
               if(tinh(r)) v = r;
               else u = r+1;
             //  printf("%d\n",r);
          }
          if(u==n) printf("-1\n");
          else printf("%d\n",u+1);
     }
    // getch();
}