Array algorithms in C++ STL

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Hello everyone!

I want to offer you a blog about the STL of C++11, a few weeks ago I was reading interesting information about this topic in GeeksforGeeks, and today I decided to share this information through this blog for all those interested. In advance, I want to thank all those who pay attention and interest to this blog, and thank any comments about it (positive or negative). Well, let's start now.

I will start with some array algorithms in the C++11 STL, which I did not know before and that can have a very interesting use, depending on the problem.

Array algorithms: these algorithms operate on an array and are useful in saving time during coding and hence useful in competitive programming as well.

all_of(): this function operates on whole range of array elements and can save time to run a loop to check each element one by on. It checks for a given property on every element and returns true when each element in range satisfies specified property, else returns false.

Code

#include "bits/stdc++.h"
using namespace std;

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  // initializing array
  vector<int> a = {1, 2, 3, 4, 5, -6};

  // checking if all elements are odds
  bool allOdds = all_of(a.begin(), a.end(), [](int x) { 
    return x % 2 != 0; 
  });

  if (allOdds) {
    cout << "All are odds numbers\n";
  } else {
    cout << "All are not odds numbers\n";
  }

  // output:
  // All are not odds numbers
}

any_of(): this function checks for a given range if there’s even one element satisfying a given property mentioned in function. Returns true if at least one element satisfies the property, else returns false.

Code

#include "bits/stdc++.h"
using namespace std;

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  // initializing array
  vector<int> a = {1, 2, 3, 4, 5, -6};

  // checking if any element is negative.
  bool anyNegative = any_of(a.begin(), a.end(), [](int x) {
    return x < 0;
  });

  if (anyNegative) {
    cout << "There are exists a negative element\n";
  } else {
    cout << "All are positive elements\n";
  }

  // output:
  // There are exists a negative element
}

none_of(): this function returns true if none of element satisfies the given condition, else returns false.

Code

#include "bits/stdc++.h"
using namespace std;

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  // initializing array
  vector<int> a = {1, 2, 3, 4, 5, -6};

  // checking if no element is negative.
  bool noNegative = none_of(a.begin(), a.end(), [](int x) {
    return x < 0; 
  });

  if (noNegative) {
    cout << "No negative elements\n";
  } else {
    cout << "There are negative element\n";
  }

  // output:
  // There are negative element
}

iota(): this function is used to assign continuous values to array.

Code

#include "bits/stdc++.h"
using namespace std;

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  // initializing array
  vector<int> a(6, 0);

  // using iota() to assign values
  iota(a.begin(), a.end(), 20);

  // displaying the new array
  cout << "The new array after assigning values is: ";

  for (auto &x: a) {
    cout << x << " \n"[&x == &a.back()];
  }

  // output:
  // The new array after assigning values is: 20 21 22 23 24 25
}

accumulate(): this function returns the sum of all the values lying in a range between [first, last) with the variable sum.

Code

#include "bits/stdc++.h"
using namespace std;

int fun(int x, int y) {
  return x * y;
}

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int initValue = 1;
  vector<int> a = {5, 10, 15};

  // simple default accumulate function
  cout << "Result using accumulate: " << accumulate(a.begin(), a.end(), initValue) << "\n";

  // using accumulate function with user-defined function
  cout << "Result using accumulate with user-defined function: " << accumulate(a.begin(), a.end(), initValue, fun) << "\n";

  // using accumulate function with pre-defined function
  cout << "Result using accumulate with pre-defined function " << accumulate(a.begin(), a.end(), initValue, minus<int>()) << "\n";

  // Output:
  // Result using accumulate: 31
  // Result using accumulate with user-defined function: 750
  // Result using accumulate with pre-defined function -29
}

Thank you to all

Comments (9)

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Pistol_Engineer

5 years ago, # |

is it applicable for c++14???????

→ Reply

EduardoBrito

5 years ago, # ^ |

Yes, it is.

KhozmoS

Thanks for share! I have a question the time complexity of those functions is linear?

FelixDzerzhinsky

all_of, any_of, none_of, accumulate, iota — O(n)

copy_n — O(cnt)

p.s. https://en.cppreference.com/w/cpp/algorithm/copy_n

ahnafrahmn

20 months ago, # |

if a[7]={1, 2, 3, 4, 5, 6, 7} Is there any easy solution or function to set a range of elements to another value? For example,

for the array a[7] up there, I want to make elements 0 from index 2 to index 5. then the array will be,

a[7]={1, 2, 0, 0, 0, 0, 7}

How can i do it without using any loops?

ishwarendra

20 months ago, # ^ |

You can use std::transform.

Any example?

std::vector a {1, 2, 3, 4, 5, 6, 7};
std::transform(std::begin(a) + 2, std::begin(a) + 6, 
               std::begin(a) + 2, [&](int x) { return 0; });

EMBailey

I think you're looking for std::fill (see cppreference for an example).

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