divide array when encountering zeroes - c++

Question

I want to divide an array into multiple(or one, maybe zero) arrays like the example below:
array = [0 1 1 2 3 4 0 3 0 3 3 0 5 6 7] -> array1 = [1 1 2 3 4] array2 = [3] array3 = [3 3] array4 = [5 6 7]
my naive approach to do this was first removing zeros from left and right then proceed to use two iterators to find the begin and end of every subarray and by using a vector constructor build the subarrays and pass them to a function. But I know for a fact that my approach is naive and inefficient so I would appreciate some suggestions on how to approach this more efficiently.
Thanks a lot guys!
also this is my code for my approach(a is the mother array):
for(int i = 0; i < a.size(); i++){
if(a[i] != 0)
break;
a.erase(a.begin() + i);
}
for(int i = a.size() - 1; i >= 0; i--){
if(a[i] != 0)
break;
a.erase(a.begin() + i);
}
auto begin = a.begin();
auto end = a.begin() + 1;
for (int i = 0; i < a.size(); i++){
if(a[i] == 0){
vector<int> temp(begin, end);
color(temp);
begin = end + 1;
end = begin + 1;
}
else end++;
}

Answer 1

One of the approach to solve this problem is to create an auxiliary array which contains index of all zero elements (in implementation const_iterator is used rather than index). This problem can be solved without creating such auxiliary array but the advantage of it is, you can find number of sub arrays are going to be created in advance. Approach is as follows,
Iterate input array and put index of zero elements in auxiliary array,
InputArray = [0, 1, 1, 2, 3, 4, 0, 3, 0, 3, 3, 0, 5, 6, 7]
Array contains zero elements index = [0, 6, 8, 11]
As you an see above there are four divider (zero index entries) which divides input array into 3 sub arrays and last zero is at index 11 and that is not last element of input array that's why one more sub array will be create so total sub arrays = 4 and for other details please see code,
#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>
using std::cout;
std::vector<std::vector<int>> splitAtZero(const std::vector<int>& arr){
std::vector<std::vector<int>::const_iterator> divider;
divider.reserve(std::max<std::size_t>(arr.size() / 4, 2));
for(std::vector<int>::const_iterator it = arr.cbegin(), endIt = arr.cend(); endIt != it; ++it){
if(0 == *it){
divider.push_back(it);
}
}
if(divider.empty()){
return {arr};
}
if(arr.size() == divider.size()){
return {};
}
std::size_t numOfSubArray = (divider.size() - 1) + (arr.cbegin() != divider.front() ? 1 : 0) +
(arr.cend() != divider.back() ? 1 : 0);
std::vector<std::vector<int>> subArr;
subArr.reserve(numOfSubArray);
std::vector<int>::const_iterator it = arr.cbegin();
for(std::vector<int>::const_iterator divderIt : divider){
if(divderIt - it > 0){
subArr.emplace_back(it, divderIt);
}
it = divderIt + 1;
}
if(arr.cend() != it){
subArr.emplace_back(it, arr.cend());
}
return subArr;
}
int main(){
std::string comma("");
for(std::vector<int>& subArr : splitAtZero({0, 1, 1, 2, 3, 4, 0, 3, 0, 3, 3, 0, 5, 6, 7})){
cout<< comma<< "[";
std::copy(subArr.cbegin(), subArr.cbegin() + (subArr.size() - 1), std::ostream_iterator<int>(cout, ", "));
cout<< subArr.back()<< "]";
comma = ", ";
}
cout<< '\n';
}
Output:
[1, 1, 2, 3, 4], [3], [3, 3], [5, 6, 7]

Answer 2

In the following approach that I propose you can retrieve the sub-arrays with a single sequential scan, with no need to exclude zeros at the beginning or at the end:
std::vector<std::vector<int>> arrays;
std::vector<int> currentArray;
for (int i = 0; i < a.size; i++)
{
if (a[i] == 0 || i == a.size - 1)
{
if (currentArray.size() != 0)
{
arrays.push_back(currentArray);
currentArray.clear();
}
}
else
{
currentArray.push_back(a[i]);
}
}