CCS sci-week (problem link http://tiny.cc/TaskSWP2019) (fb post https://www.facebook.com/ccscmu/photos/a.136488946945073/445643366029628/?type=3&theater)

0-1-check_int.cpp

#include <iostream>
using namespace std;


bool is_int(string number) {
    bool after_dot = false;
    for (char c : number) {
        if (after_dot and c != '0') {
            return false;
        } else if (c == '.') {
            after_dot = true;
        }
    }
    return true;
}


int main(void) {
    string number;
    cin >> number;
    cout << (is_int(number) ? "OK" : "NOT INTEGER") << endl;
    return 0;
}

0-2-pretty_binary.cpp

#include <iostream>
#include <algorithm>
using namespace std;


string as_bin_string_leading_zero(int number) {
    string binword;
    while (number) {
        binword.append(number % 2 ? "1" : "0");
        number /= 2;
    }
    while (binword.size() % 8) {
        binword.append("0");
    }
    reverse(binword.begin(), binword.end());
    return binword;
}


int main(void) {
    int number;
    cin >> number;
    string binword = as_bin_string_leading_zero(number);
    for (int i=0; i<binword.size(); i+=8) {
        cout << binword.substr(i, i+8) << " ";
    }
    cout << endl;
    return 0;
}

0-3-sort.cpp

#include <iostream>
#include <algorithm>
using namespace std;

int publication[100020];


int main(void) {
    int n;
    cin >> n;
    for (int i=0; i<n; i++) {
        cin >> publication[i];
    }
    sort(publication, publication+n);
    for (int i=0; i<n; i++) {
        cout << publication[i] << " ";
    }
    cout << endl;
    return 0;
}

3-6-3d_plane.cpp

#include <iostream>
using namespace std;

long pivot[3];
long matrix[3][3];


long gcd(long a, long b) {
    if (b == 0) {
        return a;
    }
    return gcd(b, a % b);
}


void swap_row(int i, int j) {
    for (int k=0; k<3; k++) {
        swap(matrix[i][k], matrix[j][k]);
    }
}


void sub_row(int i, int j) {
    for (int k=0; k<3; k++) {
        matrix[i][k] -= matrix[j][k];
    }
}


void mul_row_scalar(int i, long n) {
    for (int k=0; k<3; k++) {
        matrix[i][k] *= n;
    }
}


void make_lead_rows(int i) {
    for (int j=i+1; j<3; j++) {
        if (matrix[i][i] == 0 and matrix[j][i] != 0) {
            swap_row(i, j);
        }
    }
}


void eliminate_rows(int i) {
    for (int j=i+1; j<3; j++) {
        if (matrix[j][i] != 0) {
            long g = gcd(matrix[i][i], matrix[j][i]);
            long jg = matrix[j][i] / g;
            long ig = matrix[i][i] / g;
            mul_row_scalar(i, jg);
            mul_row_scalar(j, ig);
            sub_row(j, i);
        }
    }
}


bool is_col_zero(int i) {
    for (int k=i; k<3; k++) {
        if (matrix[i][k] != 0) {
            return false;
        }
    }
    return true;
}


bool is_plane(void) {
    for (int i=0; i<3; i++) {
        if (is_col_zero(i)) {
            return true;
        }
        make_lead_rows(i);
        eliminate_rows(i);
    }
    return false;
}


int main(void) {
    int t;
    cin >> t;
    for (int i=0; i<t; i++) {
        for (int k=0; k<3; k++) {
            cin >> pivot[k];
        }
        for (int j=0; j<3; j++) {
            for (int k=0; k<3; k++) {
                cin >> matrix[j][k];
                matrix[j][k] -= pivot[k];
            }
        }
        cout << (is_plane() ? "YES" : "NO") << endl;
    }
    return 0;
}

3-7-fib_word.cpp

#include <iostream>
using namespace std;

long fibs[90];


void init_fibs(void) {
    fibs[0] = -1;
    fibs[1] = 1;
    fibs[2] = 1;
    for (int i=3; i<90; i++) {
        fibs[i] = fibs[i-1] + fibs[i-2];
    }
}


char find_fib_char(int n, long k) {
    if (n == 1) {
        return 'A';
    }
    if (n == 2) {
        return 'B';
    }
    if (k <= fibs[n-2]) {
        return find_fib_char(n-2, k);
    } else {
        return find_fib_char(n-1, k-fibs[n-2]);
    }
}


int main(void) {
    init_fibs();
    int t;
    cin >> t;
    for (int i=0; i<t; i++) {
        int n;
        long k;
        cin >> n >> k;
        cout << find_fib_char(n, k) << endl;
    }
    return 0;
}