What's Test 9?

I saw, that Test 9:
7
1 3
2 5
2 5
4 7
6 9
6 9
8 10

My answer:
3
1 3
4 7
8 10

What's correct answer?

My program runs any tests from other topics perfectly, but something is wrong with the task 1. Sounds like madness.

Edited by author 24.02.2022 23:04

Edited by author 24.02.2022 23:05

What is test #3??

I got WA in first test. I checked my program using a lot of compiler and in first test my program outputs is correct.

my code id:9308865

Hello. My program passes all tests from the forum, but I still get WA6.

I do brute force

First, I go through all the elements that are to the right of the current one, then everything that is to the left

can anyone have any tests?

here is y code is needed:

#include <iostream>

using namespace std;

int n, result = 0, sizeHelpArray = 0, sizeAnswerArray;
int line[100][2], helpArray[100][2], answerArray[100][2];

//initialization and sorting on the left border
void Init()
{
    int i, j;
    cin >> n;
    for (i = 0; i < n; i++)
    {
        cin >> line[i][0] >> line[i][1];
        if (line[i][0] > line[i][1])
            swap(line[i][0], line[i][1]);
    }

    for (i = 0; i < n; i++)
    {
        for (j = i + 1; j < n; j++)
        {
            if (line[j][0] < line[i][0])
            {
                swap(line[i][0], line[j][0]);
                swap(line[i][1], line[j][1]);
            }
            if(line[j][0] == line[i][0])
                if (line[j][1] < line[i][1])
                {
                    swap(line[i][0], line[j][0]);
                    swap(line[i][1], line[j][1]);
                }
        }
    }
}

//adding a segment to the temporary answer

void AddInHelpArray(int index)
{
    sizeHelpArray++;
    helpArray[sizeHelpArray][0] = line[index][0];
    helpArray[sizeHelpArray][1] = line[index][1];
}

//to record the best current result

void copyInAnswerArray()
{
    int i;
    for (i = 0; i < sizeHelpArray + 1; i++)
    {
        answerArray[i][0] = helpArray[i][0];
        answerArray[i][1] = helpArray[i][1];
    }
}

void sortAnswerArray()
{
    for (int i = 0; i <= sizeAnswerArray; i++)
    {
        for (int j = i + 1; j <= sizeAnswerArray; j++)
        {
            if (answerArray[j][0] < answerArray[i][0])
            {
                swap(answerArray[i][0], answerArray[j][0]);
                swap(answerArray[i][1], answerArray[j][1]);
            }
            if (answerArray[j][0] == answerArray[i][0])
                if (answerArray[j][1] < answerArray[i][1])
                {
                    swap(answerArray[i][0], answerArray[j][0]);
                    swap(answerArray[i][1], answerArray[j][1]);
                }
        }
    }
}

void Solve()
{
    int i, x, tmp = 1, currentPoint;
        //starting from the first element ..
    for (x = 0; x < n; x++)
    {
        sizeHelpArray = 0;
        tmp = 1;
        memset(helpArray, 0, sizeof(helpArray));
                //I write the current element to an auxiliary array
        helpArray[sizeHelpArray][0] = line[x][0];
        helpArray[sizeHelpArray][1] = line[x][1];
        currentPoint = line[x][1];
                //Checking items to the right of the current one
        for (i = x + 1; i < n; i++)
        {
            if (line[i][0] >= currentPoint)
            {
                tmp++;
                currentPoint = line[i][1];
                AddInHelpArray(i);
            }
        }


        currentPoint = line[x][0];
        int border;
        border = line[x][0];
        bool first = true;
                //Checking items to the left of the current one
        for (int j = 0; j < x; j++)
        {
            if (line[j][1] <= currentPoint && first)
            {
                tmp++;
                currentPoint = line[j][1];
                AddInHelpArray(j);
                first = false;
            }
            else if (first == false && line[j][0] >= currentPoint && line[j][1] <= border)
            {
                tmp++;
                currentPoint = line[j][1];
                AddInHelpArray(j);
            }
        }
                //If the result is better than the previous one, then I save it.
        if (tmp > result)
        {
            result = tmp;
            copyInAnswerArray();
            sizeAnswerArray = sizeHelpArray;
        }
    }

    sortAnswerArray();
    cout << result << endl;
    for (int i = 0; i <= sizeAnswerArray; i++)
        cout << answerArray[i][0] << " " << answerArray[i][1] << endl;
}

int main()
{
    Init();
    Solve();
    return 0;
}

Edited by author 02.04.2021 07:26

Edited by author 02.04.2021 07:26

Edited by author 02.04.2021 07:37

Edited by author 02.04.2021 07:37

I use some shamanism ang get AC. Lets see to the next test:

6
0 20
10 50
30 100
60 120
70 130
110 140

my AC prog outputs:

2
10 50
110 140

but right answer of course is:

3
0 20
30 100
110 140

Your tests must be stronger

6
1 5
2 6
3 7
4 8
5 9
6 10

WHY answer is:
2
1 5
5 9
I think [2;6] and [3;7] have common interior point such as 3, 4, 5, 6.

Does anyone know the 8th test?

Solved both tasks with the same algorithm. Think this task is over-valued.

Edited by author 26.10.2016 20:59

If you're doing a greedy solution and you're sorting by the rightmost endpoints (B_i), you need to sort with the leftmost endpoints as second key. That is, if B_i == B_j, the shortest segment of i and j goes first in the list.

This basically means that longer segments are kept, so for inputs:

3
3 5
1 5
5 6

You would get result
2
1 5
5 6

instead of
2
3 5
5 6

which means you get a bigger covering of the set but the problem statement didn't mention this requirement.

Edited by author 24.12.2014 21:07

Change "left" to "remaining" since it would otherwise indicate "the opposite of right" which is confusing

Is there somebody who can give me input data for test #2?

What's Test 9?

My algo is:
Search the segment with more intersections and delete it (repeat while the segment got 0 intersections)
Is it wrong?

If you have a problem - WA4 - consider sorting input, not output

for example:

5
1 5
3 6
1 3
9 6
4 2

answer
3
1 3
3 6
6 9

Edited by author 03.11.2013 17:06

This problem is quite easy.You can sort the "end node",and then use the greedy algo to solve the program.

Please tell me the reason or give me the t4,thank you!
This is my program:
#include <cstdio>
#include <iostream>
#include <cstring>
using namespace std;
int n,result=0,xia=0,rxia;
int line[110][2],era[110][2],fera[110][2];
void init()
{
  int i,j;
  scanf("%d",&n);
  for(i=1;i<=n;i++)
  {
    scanf("%d %d",&line[i][0],&line[i][1]);
    if(line[i][0]>line[i][1])
      swap(line[i][0],line[i][1]);
  }
  for(i=1;i<n;i++)
    for(j=i+1;j<=n;j++)
    {
      if(line[j][0]<line[i][0])
      {
        swap(line[i][0],line[j][0]);
        swap(line[i][1],line[j][1]);
      }
      if(line[j][0]==line[i][0])
        if(line[j][1]<line[i][1])
        {
          swap(line[i][0],line[j][0]);
          swap(line[i][1],line[j][1]);
        }
    }
}
void jilu(int i)
{
  xia++;
  era[xia][0]=line[i][0];
  era[xia][1]=line[i][1];
}
void copyera()
{
  int i;
  for(i=1;i<=xia;i++)
  {
    fera[i][0]=era[i][0];
    fera[i][1]=era[i][1];
  }
}
void solve()
{
  int i,x,temp=1,now;
  for(x=1;x<=n;x++)
  {
    xia=0;
    temp=1;
    memset(era,0,sizeof(era));
    xia++;
    era[xia][0]=line[x][0];
    era[xia][1]=line[x][1];
    now=line[x][1];
    for(i=x+1;i<=n;i++)
      if(line[i][0]>=now)
      {
        temp++;
        now=line[i][1];
        jilu(i);
      }
    if(temp>result)
    {
      result=temp;
      copyera();
      rxia=xia;
    }
  }
  printf("%d\n",result);
  for(i=1;i<=rxia;i++)
    printf("%d %d\n",fera[i][0],fera[i][1]);
}
int main()
{
  init();
  solve();
  return(0);
}

Thank you very much!!!

I got AC, but on test:

6
0 30
10 70
20 80
40 110
90 130
120 140

my AC program output:
2
0 30
90 130

but answer must be:
3
0 30
40 110
120 140

Any one who can give some hint? Thanks

maybe you forgot to write how many lines should be saved.
sorry for my poor English