functions.cpp

#include "functions.h"
#include <algorithm>
#include <cmath>

int sumDigits(const vector<int>& arr) {
    int sum = 0;
    for (int x : arr) {
        int t = abs(x);
        while (t > 0) {
            sum += t % 10;
            t /= 10;
        }
    }
    return sum;
}

double averagePositive(const vector<int>& arr) {
    double s = 0;
    int k = 0;
    for (int x : arr) {
        if (x > 0) {
            s += x;
            k++;
        }
    }
    if (k == 0) return 0;
    return s / k;
}

pair<int,int> maxNegative(const vector<int>& arr) {
    int best = -1000000;
    int pos = -1;
    for (int i = 0; i < arr.size(); i++) {
        if (arr[i] < 0 && arr[i] > best) {
            best = arr[i];
            pos = i;
        }
    }
    return {best, pos};
}

int mostFrequent(const vector<int>& arr) {
    int bestValue = arr[0];
    int bestCount = 0;
    for (int i = 0; i < arr.size(); i++) {
        int c = 0;
        for (int j = 0; j < arr.size(); j++)
            if (arr[i] == arr[j]) c++;
        if (c > bestCount) {
            bestCount = c;
            bestValue = arr[i];
        }
    }
    return bestValue;
}

int maxOddIndexDiv3(const vector<int>& arr) {
    int best = -1000000;
    bool found = false;
    for (int i = 1; i < arr.size(); i += 2) {
        if (arr[i] % 3 == 0) {
            if (!found || arr[i] > best) {
                best = arr[i];
                found = true;
            }
        }
    }
    if (!found) return 0;
    return best;
}

void swapMaxEvenMinOdd(vector<int>& arr) {
    int maxEven = -1000000, posEven = -1;
    int minOdd = 1000000, posOdd = -1;

    for (int i = 0; i < arr.size(); i++) {
        if (arr[i] % 2 == 0 && arr[i] > maxEven) {
            maxEven = arr[i];
            posEven = i;
        }
        if (arr[i] % 2 != 0 && arr[i] < minOdd) {
            minOdd = arr[i];
            posOdd = i;
        }
    }

    if (posEven == -1 || posOdd == -1) {
        for (int i = 0; i < arr.size(); i++)
            arr[i] = 0;
    } else {
        int t = arr[posEven];
        arr[posEven] = arr[posOdd];
        arr[posOdd] = t;
    }
}

vector<int> intersectionArr(const vector<int>& a, const vector<int>& b) {
    vector<int> r;
    for (int x : a)
        for (int y : b)
            if (x == y) r.push_back(x);

    sort(r.begin(), r.end());
    r.erase(unique(r.begin(), r.end()), r.end());
    return r;
}

vector<int> diffArr(const vector<int>& a, const vector<int>& b) {
    vector<int> r;

    for (int x : a) {
        bool ok = true;
        for (int y : b)
            if (x == y) ok = false;
        if (ok) r.push_back(x);
    }

    for (int y : b) {
        bool ok = true;
        for (int x : a)
            if (x == y) ok = false;
        if (ok) r.push_back(y);
    }

    return r;
}

functions.h

#ifndef FUNCTIONS_H
#define FUNCTIONS_H

#include <vector>
using namespace std;

int sumDigits(const vector<int>& arr);
double averagePositive(const vector<int>& arr);
pair<int,int> maxNegative(const vector<int>& arr);
int mostFrequent(const vector<int>& arr);
int maxOddIndexDiv3(const vector<int>& arr);
void swapMaxEvenMinOdd(vector<int>& arr);
vector<int> intersectionArr(const vector<int>& a, const vector<int>& b);
vector<int> diffArr(const vector<int>& a, const vector<int>& b);

#endif

main.cpp

#include <iostream>
#include <vector>
#include "functions.h"
using namespace std;

int main() {
    vector<int> arr{12, 104, 81, -5, -10, 3, 9, 9};

    cout << sumDigits(arr) << endl;
    cout << averagePositive(arr) << endl;

    auto neg = maxNegative(arr);
    cout << neg.first << " " << neg.second << endl;

    cout << mostFrequent(arr) << endl;
    cout << maxOddIndexDiv3(arr) << endl;

    swapMaxEvenMinOdd(arr);
    for (int x : arr) cout << x << " ";
    cout << endl;

    vector<int> a{1,2,3,4,5};
    vector<int> b{4,5,6,7};

    vector<int> both = intersectionArr(a, b);
    for (int x : both) cout << x << " ";
    cout << endl;

    vector<int> one = diffArr(a, b);
    for (int x : one) cout << x << " ";
    cout << endl;

    return 0;
}