Task: Cheryl's birthday
C++: #include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

const vector<string> MONTHS = {
    "Jan", "Feb", "Mar", "Apr", "May", "Jun",
    "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};

struct Birthday {
    int month, day;

    friend ostream &operator<<(ostream &, const Birthday &);
};

ostream &operator<<(ostream &out, const Birthday &birthday) {
    return out << MONTHS[birthday.month - 1] << ' ' << birthday.day;
}

template <typename C>
bool monthUniqueIn(const Birthday &b, const C &container) {
    auto it = cbegin(container);
    auto end = cend(container);
    int count = 0;
    while (it != end) {
        if (it->month == b.month) {
            count++;
        }
        it = next(it);
    }
    return count == 1;
}

template <typename C>
bool dayUniqueIn(const Birthday &b, const C &container) {
    auto it = cbegin(container);
    auto end = cend(container);
    int count = 0;
    while (it != end) {
        if (it->day == b.day) {
            count++;
        }
        it = next(it);
    }
    return count == 1;
}

template <typename C>
bool monthWithUniqueDayIn(const Birthday &b, const C &container) {
    auto it = cbegin(container);
    auto end = cend(container);
    while (it != end) {
        if (it->month == b.month && dayUniqueIn(*it, container)) {
            return true;
        }
        it = next(it);
    }
    return false;
}

int main() {
    vector<Birthday> choices = {
        {5, 15}, {5, 16}, {5, 19}, {6, 17}, {6, 18},
        {7, 14}, {7, 16}, {8, 14}, {8, 15}, {8, 17},
    };

    
    
    vector<Birthday> filtered;
    for (auto bd : choices) {
        if (!monthUniqueIn(bd, choices)) {
            filtered.push_back(bd);
        }
    }

    
    
    vector<Birthday> filtered2;
    for (auto bd : filtered) {
        if (!monthWithUniqueDayIn(bd, filtered)) {
            filtered2.push_back(bd);
        }
    }

    
    
    vector<Birthday> filtered3;
    for (auto bd : filtered2) {
        if (dayUniqueIn(bd, filtered2)) {
            filtered3.push_back(bd);
        }
    }

    
    
    vector<Birthday> filtered4;
    for (auto bd : filtered3) {
        if (monthUniqueIn(bd, filtered3)) {
            filtered4.push_back(bd);
        }
    }

    if (filtered4.size() == 1) {
        cout << "Cheryl's birthday is " << filtered4[0] << '\n';
    } else {
        cout << "Something went wrong!\n";
    }

    return 0;
}

Python: 

from itertools import groupby
from re import split



def main():
    

    month, day = 0, 1
    print(
        
        
        uniquePairing(month)(
            
            
            uniquePairing(day)(
                
                
                monthsWithUniqueDays(False)([
                    
                    tuple(x.split()) for x in
                    split(
                        ', ',
                        'May 15, May 16, May 19, ' +
                        'June 17, June 18, ' +
                        'July 14, July 16, ' +
                        'Aug 14, Aug 15, Aug 17'
                    )
                ])
            )
        )
    )





def monthsWithUniqueDays(blnInclude):
    
    def go(xs):
        month, day = 0, 1
        months = [fst(x) for x in uniquePairing(day)(xs)]
        return [
            md for md in xs
            if blnInclude or not (md[month] in months)
        ]
    return go



def uniquePairing(i):
    
    def go(xs):
        def inner(md):
            dct = md[i]
            uniques = [
                k for k in dct.keys()
                if 1 == len(dct[k])
            ]
            return [tpl for tpl in xs if tpl[i] in uniques]
        return inner
    return ap(bindPairs)(go)





def bindPairs(xs):
    
    return lambda f: f(
        (
            dictFromPairs(xs),
            dictFromPairs(
                [(b, a) for (a, b) in xs]
            )
        )
    )



def dictFromPairs(xs):
    
    return {
        k: [snd(x) for x in m] for k, m in groupby(
            sorted(xs, key=fst), key=fst
        )
    }





def ap(f):
    
    def go(g):
        def fxgx(x):
            return f(x)(
                g(x)
            )
        return fxgx
    return go



def fst(tpl):
    
    return tpl[0]



def snd(tpl):
    
    return tpl[1]


if __name__ == '__main__':
    main()