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# Error in code: Read access violation

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Problem: Given n segments, it is necessary to find a set of points of the minimum size for which each of the segments contains at least one of the points.

The first line contains the number 1≤n≤100 segments. Each of the next n lines contains two numbers 0≤l≤r≤109, specifying the beginning and end of the segment. Print the optimal number of m points and the m points themselves. If there are several such sets of points, print any of them.

My solution:

``````void swap (int * a1, int * a2, int M);
void sort (int ** a, int N, int M);
void greedy (int ** a, int * x, int N);
int main ()
{
int ** a; // two-dimensional array of segments
int N;
int M = 2;
int * x; // one-dimensional array of points
cout & lt; & lt; "Enter N:"; // enter the number of segments
cin & gt; & gt; N;
x = new int [N]; // initialize an array, which will later become an array of points
for (int i = 0; i & lt; N; i ++)
x [i] = 0;
a = new int * [N];
for (int i = 0; i & lt; N; i ++)
a [i] = new int [M];
// enter the ends of the segments
for (int i = 0; i & lt; N; i ++)
{
for (int j = 0; j & lt; M; j ++)
{
cin & gt; & gt; a [i] [j];
}
}
// output before sorting
cout & lt; & lt; endl & lt; & lt; "Before sorting:" & lt; & lt; endl;
for (int i = 0; i & lt; N; i ++)
{
for (int j = 0; j & lt; M; j ++)
cout & lt; & lt; std :: setw (3) & lt; & lt; a [i] [j] & lt; & lt; "";
cout & lt; & lt; endl;
}
sort (a, N, M); // sort the array
// output after sorting
cout & lt; & lt; endl & lt; & lt; "After sorting:" & lt; & lt; endl;
for (int i = 0; i & lt; N; i ++)
{
for (int j = 0; j & lt; M; j ++)
cout & lt; & lt; setw (3) & lt; & lt; a [i] [j] & lt; & lt; "";
cout & lt; & lt; endl;
}
// call a function with a greedy algorithm
greedy (a, x, N);
for (int i = 0; i & lt; = N; i ++)
cout & lt; & lt; x [i] & lt; & lt; ' ';
system ("pause");
return 0;
}
void swap (int * a1, int * a2, int M) // swaps 2 lines
{
for (int i = 0; i & lt; M; i ++)
{
int temp = a1 [i];
a1 [i] = a2 [i];
a2 [i] = temp;
}
}
void sort (int ** a, int N, int M) // bubble sorting of segments by the right point
{
for (int i = 0; i & lt; N; i ++)
for (int j = N - 1; j & gt; i; j--)
if (a [j - 1]  & gt; a [j] )
swap (a [j - 1], a [j], M);
}
void greedy (int ** a, int * x, int N)
{
int i = 0;
int k = 0;
while (i & lt; = N)
{
x [k] = a [i] ;
i ++;
while ((x [k] & gt; = a [i] ) & amp; & amp; (x [k] & lt; = a [i] ))
{i ++;}
k ++;
}
}
``````

But the program crashes with an error: Read access violation. Maybe someone sees why?

Again tasks from the stepik from the Algorithms course. Guys, you are learning for yourself, try to figure it out for yourself.

The crux of the problem is obvious: you ran out of the array. I see three places where this happens:

``````// N is the size, the last index is N-1, therefore strictly less than N
while (i & lt; = N)
``````

is similar here:

``````for (int i = 0; i & lt; = N; i ++)
``````

here a little differently:

``````// Thinking outside the array of zeros?
// And who promises?
// Any trash can be there, so you can run far. Check i too.
while ((x [k] & gt; = a [i] ) & amp; & amp; (x [k] & lt; = a [i] ))
{i ++;}
``````

Well, return from `greedy ``k `to find out the number of points.

And yes, I recommend making a structure with two fields for a segment: you will not bother with a two-dimensional array, the code will become more readable, and as a result, it is easier to look for errors in such code. And also give meaningful names to variables. What prevents `x `from being named `dots `or `points `, and `a ``lines `, I already I’m not talking about the passionate desire for manual memory management, instead of `std :: vector `.

Well, learn how to use debuggers and profilers like Valgrind, they will almost poke you where you have an error.

You are out of range when i = N, correct in & lt; = loops to & lt ;.

`cout `, `cin `, `system ("pause") `work with the external environment – if the problem is with them, comment out the calls.

But it looks more like an error somewhere in the sizes of arrays and accessing an element outside of them.

I recommend that you use the debugger and publish all error details.

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