Suppose I have an array: int list[] = {1, 2, 4, 5, 6};
and I want to shift the array from the middle to the right and place 3 in the place of 4 so it would look like: {1, 2, 3, 4, 5, 6}.
How would I do it?
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2 Answers
If you can use the C++ Standard Library, then std::vector is a replacement for arrays. It has a dedicated method insert to do what you want:
std::vector<int> v;
... // add elements 1, 2, 4, 5, 6 to it
v.insert(v.begin() + 2, 3); // insert 3 at position 2
This is good if you know where to insert your new element. However, it seems that your list should always be sorted, and you want to insert the new element so it remains sorted. If so, you better use std::multiset:
std::multiset<int> v;
... // add elements 1, 2, 4, 5, 6 to it
v.insert(3); // insert 3
Here, you don't need to tell where to insert the new element.
Comments
If you cannot use vector, one solution is:
Create an array with a lot of space (with a few empty positions at the end);
int * array = malloc(sizeof(int) * array_size);Use two variables one to save the size of the array (lets called
size) another to count the number of elements already added (lets callednumber_of_elements_in_the_array)
When you added an element at the position 'x', you do the following (with x < size of the array):
int tmp = array[x]; // save the current value
array[x] = new_value; // update with the new value
int tmp2;
number_of_elements_in_the_array++;
// we reach the limited
if(number_of_elements_in_the_array == size)
{
size = 2 * size; //lets double that size
int *new_array = malloc(sizeof(int) * size);
// copy the first elements
for(int i = 0; i <= x; i++)
new_array[i] = array[i];
new_array[x+1] = tmp;
// copy the last elements
for(int i = x+1; i < number_of_elements_in_the_array; i++)
new_array[i+1] = array[i];
free(array) // free the old space
array = new_array; // update the new pointer
}
else
{
// shift the remaining elements
for(int i = x+1; i < number_of_elements_in_the_array; i++)
{
tmp2 = array[i];
array[i] = tmp;
tmp = tmp2;
}
}
when you reach the limited, create a new array with more memory, copy from the old array to the new one, and update the variables number_of_elements_in_the_array and size accordingly.
Disclaimer : I didn't tested, thus it might be some minor erros, but the overall ideia is there.