How to define the begin and the end value in C++? - c++

Question

I have an array like this:
600
250
600
600
600
I want to define the begin and the end indexes of this array where the value is greather than 500.
I made a variable which value is 2, because there are two section in my array where the values are greather than 500 (1-1 and 3-5).
So how could I output this:
1 1 3 5
The first 1 means the begin index is 1, the second 1 means the end index is also 1.
The 3 means the next section begin index where the value is greather than 500 is 3.
And the 5 means the end index of the second section is 5.

Answer 1

Using std:
std::vector<std::pair<std::size_t, std::size_t>>
compute_range_greater_than(const std::vector<int>& v, int threshold)
{
std::vector<std::pair<std::size_t, std::size_t>> res;
for (auto it = v.begin(); it != v.end(); /*Empty*/)
{
auto beg = std::find_if(it, v.end(), [=](int i) { return !(i < threshold); });
if (beg == v.end()) {
return res;
}
it = std::find_if(beg, v.end(), [=](int i) { return i < threshold; });
// using 1-index
res.push_back({1 + std::distance(v.begin(), beg), std::distance(v.begin(), it)});
}
return res;
}
Live Demo

Answer 2

Try this:
#include <iostream>
#include <vector>
int main()
{
std::vector<int> v;
v.push_back(10);
v.push_back(200);
v.push_back(170);
v.push_back(160);
v.push_back(20);
v.push_back(300);
v.push_back(12);
v.push_back(230);
std::vector<int> indexes;
int limit = 150;
bool started = false;
for (int i = 0; i < v.size(); i++)
{
int value = v[i];
if (value > limit && !started)
{
started = true;
indexes.push_back(i);
}
else if (value < limit && started)
{
started = false;
indexes.push_back(i - 1);
}
}
if (started)
indexes.push_back(v.size() - 1);
for (int i = 0; i < indexes.size(); i++)
{
if (i % 2 == 0)
std::cout << indexes[i] << "-";
else
std::cout << indexes[i] << "; ";
}
return 0;
}
Here limit is 150, but you can change it. Output is
1-3; 5-5; 7-7;
Good luck :)

Answer 3

You really should consider improving your question by better explaining what you want to do and by providing code that you already wrote (and if you didnt you should do it). However, I am in a good mood, so here you go:
#include <vector>
#include <iostream>
struct BeginAndEndIndex{
int begin;
int end;
BeginAndEndIndex(int begin) : begin(begin),end(begin) {}
};
typdef std::vector<BeginAndEndIndex> IndexV;
typdef std::vector<int> IV;
IndexV findBeginAndEndIndex(const IV& in,int threshold){
IndexV result;
bool isBiggerThanThreshold = false;
for (int i=0;i<in.size();i++){
if (!isBiggerThanThreshold) {
if (in[i]>threshold){
result.push_back(BeginAndEndIndex(i));
isBiggerThanThreshold = true;
}
} else {
if (in[i]<threshold){
result.back().end = i-1;
isBiggerThanThreshold = false;
}
}
}
if (isBiggerThanThreshold){result.back().end = in.size()-1;}
return result;
}
int main(void) {
IV foo {600,250,600,600,600};
IndexV bar = findBeginAndEndIndex(foo,500);
for (int i=0;i<bar.size();i++){
std::cout << bar[i].begin << " " << bar[i].end << std::endl;
}
return 0;
}
I am pretty sure that there is a more elegant way to implement it by using std::algorithms.

Answer 4

Just in straight C and not storing the indices anywhere, the following code produces the exact output that you are asking for:
#include <stdio.h>
int main(int argc, char **argv)
{
int values[] = {600, 250, 600, 600, 600};
int threshhold = 500;
int begIndex = -1;
int endIndex = -1;
int i;
for (i = 0; i < sizeof(values)/sizeof(values[0]); i++)
{
if (values[i] > threshhold)
{
if (begIndex < 0)
{
begIndex = i;
}
endIndex = i;
}
else if (begIndex >= 0)
{
printf("%d %d ", begIndex + 1, endIndex + 1);
begIndex = endIndex = -1;
}
}
if (begIndex >= 0)
printf("%d %d", begIndex + 1, endIndex + 1);
printf("\n");
return 0;
}
Keep in mind the arrays in C/C++ start at zero, not one. Changing the above code to store the begIndex and endIndex pairs should be a trivial operation.