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;
}

Go: package main

import (
    "fmt"
    "time"
)

type birthday struct{ month, day int }

func (b birthday) String() string {
    return fmt.Sprintf("%s %d", time.Month(b.month), b.day)
}

func (b birthday) monthUniqueIn(bds []birthday) bool {
    count := 0
    for _, bd := range bds {
        if bd.month == b.month {
            count++
        }
    }
    if count == 1 {
        return true
    }
    return false
}

func (b birthday) dayUniqueIn(bds []birthday) bool {
    count := 0
    for _, bd := range bds {
        if bd.day == b.day {
            count++
        }
    }
    if count == 1 {
        return true
    }
    return false
}

func (b birthday) monthWithUniqueDayIn(bds []birthday) bool {
    for _, bd := range bds {
        if bd.month == b.month && bd.dayUniqueIn(bds) {
            return true
        }
    }
    return false
}

func main() {
    choices := []birthday{
        {5, 15}, {5, 16}, {5, 19}, {6, 17}, {6, 18},
        {7, 14}, {7, 16}, {8, 14}, {8, 15}, {8, 17},
    }

    
    
    var filtered []birthday
    for _, bd := range choices {
        if !bd.monthUniqueIn(choices) {
            filtered = append(filtered, bd)
        }
    }

    
    
    var filtered2 []birthday
    for _, bd := range filtered {
        if !bd.monthWithUniqueDayIn(filtered) {
            filtered2 = append(filtered2, bd)
        }
    }

    
    
    var filtered3 []birthday
    for _, bd := range filtered2 {
        if bd.dayUniqueIn(filtered2) {
            filtered3 = append(filtered3, bd)
        }
    }

    
    
    var filtered4 []birthday
    for _, bd := range filtered3 {
        if bd.monthUniqueIn(filtered3) {
            filtered4 = append(filtered4, bd)
        }
    }

    if len(filtered4) == 1 {
        fmt.Println("Cheryl's birthday is", filtered4[0])
    } else {
        fmt.Println("Something went wrong!")
    }
}