Solving "Quesito con la Susi n. 946"

susi946.cpp

/* This trivially solves a quiz on the Italian magazine
   "La Settimana Enigmistica", namely
   "Quesito con la Susi n. 946".

   It uses, without any special reason, >C++11
   features.

   Problem: 
     There are four friends (Giovanni, Marco, Simone, Elisa)
     sat down behind a desk; Susi must say who's the shortest
     taking into account their statements and the fact that one
     among Giovanni, Marco and Simone, always lies.

     Marco says he's taller than Giovanni;
     Giovanni says he's shorter than Simone;
     Simone says that Giovanni is the shortest.

     (Elisa says that only one of the other three lies)

   Output:
     Elisa Giovanni Marco Simone 
     Elisa Giovanni Simone Marco

   That means, Elisa is the shortest.
*/
#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
#include <string>
#include <initializer_list>

typedef std::vector<std::string> arg0;
typedef std::function<bool(arg0)> chk_func;

// returns the (supposed) height of s (given by its
// position into the vector: the higher the index, the taller
// the person. (s must exist in n)
int h(const arg0& n, const std::string& s)
{
    return std::find(n.begin(), n.end(), s) - n.begin();
}

// collection of statements which must all hold
class Checker
{
private:
    std::vector<chk_func> s_;
public:
    Checker(std::initializer_list<chk_func> cks) : s_(cks) {}

    bool operator()(const arg0& p) const {
        return std::all_of(s_.cbegin(), s_.cend(),
                           [&p](chk_func f) -> bool { return f(p); });
    }
};

void dump(const arg0& names)
{
    for (const auto& name : names) {
        std::cout << name << " ";
    }
    std::cout << "\n";
}

int main()
{    
    arg0 names{"Giovanni", "Marco", "Elisa", "Simone"};

    // sorting just because of std::next_permutation()
    std::sort(names.begin(), names.end());

    // statements
    chk_func f1 = [](const arg0& n) -> bool {
        return h(n, "Marco") > h(n, "Giovanni");
    };
    
    chk_func f2 = [](const arg0& n) -> bool {
        return h(n, "Giovanni") < h(n, "Simone");
    };
    
    chk_func f3 = [](const arg0& n) -> bool {
        return
               h(n, "Giovanni") < h(n, "Simone") &&
               h(n, "Giovanni") < h(n, "Marco") &&
               h(n, "Giovanni") < h(n, "Elisa");
    };

    // in each set of statements we are negating the
    // statement of the person who's supposedly lying.
    std::vector<Checker> checklist{
        Checker{f1, f2, std::not1(f3)},
        Checker{f1, std::not1(f2), f3},
        Checker{std::not1(f1), f2, f3}
    };

    do {
        for (const auto& check : checklist) {
            if (check(names)) {
                // dump the vector in its current permutation
                dump(names);
            }
        }
    } while (std::next_permutation(names.begin(), names.end()));
    
    return 0;
}