Task: Stable marriage problem
C++: #include <algorithm>
#include <iostream>
#include <map>
#include <queue>
#include <string>
#include <vector>
using namespace std;

const char *men_data[][11] = {
    { "abe",  "abi","eve","cath","ivy","jan","dee","fay","bea","hope","gay" },
    { "bob",  "cath","hope","abi","dee","eve","fay","bea","jan","ivy","gay" },
    { "col",  "hope","eve","abi","dee","bea","fay","ivy","gay","cath","jan" },
    { "dan",  "ivy","fay","dee","gay","hope","eve","jan","bea","cath","abi" },
    { "ed",   "jan","dee","bea","cath","fay","eve","abi","ivy","hope","gay" },
    { "fred", "bea","abi","dee","gay","eve","ivy","cath","jan","hope","fay" },
    { "gav",  "gay","eve","ivy","bea","cath","abi","dee","hope","jan","fay" },
    { "hal",  "abi","eve","hope","fay","ivy","cath","jan","bea","gay","dee" },
    { "ian",  "hope","cath","dee","gay","bea","abi","fay","ivy","jan","eve" },
    { "jon",  "abi","fay","jan","gay","eve","bea","dee","cath","ivy","hope" }
};
 
const char *women_data[][11] = {
    { "abi",  "bob","fred","jon","gav","ian","abe","dan","ed","col","hal" },
    { "bea",  "bob","abe","col","fred","gav","dan","ian","ed","jon","hal" },
    { "cath", "fred","bob","ed","gav","hal","col","ian","abe","dan","jon" },
    { "dee",  "fred","jon","col","abe","ian","hal","gav","dan","bob","ed" },
    { "eve",  "jon","hal","fred","dan","abe","gav","col","ed","ian","bob" },
    { "fay",  "bob","abe","ed","ian","jon","dan","fred","gav","col","hal" },
    { "gay",  "jon","gav","hal","fred","bob","abe","col","ed","dan","ian" },
    { "hope", "gav","jon","bob","abe","ian","dan","hal","ed","col","fred" },
    { "ivy",  "ian","col","hal","gav","fred","bob","abe","ed","jon","dan" },
    { "jan",  "ed","hal","gav","abe","bob","jon","col","ian","fred","dan" }
};

typedef vector<string> PrefList;
typedef map<string, PrefList> PrefMap;
typedef map<string, string> Couples;


bool prefers(const PrefList &prefer, const string &first, const string &second)
{
    for (PrefList::const_iterator it = prefer.begin(); it != prefer.end(); ++it)
    {
        if (*it == first) return true;
        if (*it == second) return false;
    }
    return false; 
}

void check_stability(const Couples &engaged, const PrefMap &men_pref, const PrefMap &women_pref)
{
    cout << "Stablility:\n";
    bool stable = true;
    for (Couples::const_iterator it = engaged.begin(); it != engaged.end(); ++it)
    {
        const string &bride = it->first;
        const string &groom = it->second;
        const PrefList &preflist = men_pref.at(groom);

        for (PrefList::const_iterator it = preflist.begin(); it != preflist.end(); ++it)
        {
            if (*it == bride) 
                break;
            if (prefers(preflist, *it, bride) && 
                prefers(women_pref.at(*it), groom, engaged.at(*it))) 
            {
                cout << "\t" << *it <<
                    " prefers " << groom <<
                    " over " << engaged.at(*it) <<
                    " and " << groom <<
                    " prefers " << *it <<
                    " over " << bride << "\n";
                stable = false;
            }
        }
    }
    if (stable) cout << "\t(all marriages stable)\n";
}

int main()
{
    PrefMap men_pref, women_pref;
    queue<string> bachelors;

    
    for (int i = 0; i < 10; ++i) 
    {
        for (int j = 1; j < 11; ++j) 
        {
              men_pref[  men_data[i][0]].push_back(  men_data[i][j]);
            women_pref[women_data[i][0]].push_back(women_data[i][j]);
        }
        bachelors.push(men_data[i][0]);
    }

    Couples engaged; 

    cout << "Matchmaking:\n";
    while (!bachelors.empty())
    {
        const string &suitor = bachelors.front();
        const PrefList &preflist = men_pref[suitor];

        for (PrefList::const_iterator it = preflist.begin(); it != preflist.end(); ++it)
        {
            const string &bride = *it;

            if (engaged.find(bride) == engaged.end()) 
            {
                cout << "\t" << bride << " and " << suitor << "\n";
                engaged[bride] = suitor; 
                break;
            }

            const string &groom = engaged[bride];

            if (prefers(women_pref[bride], suitor, groom))
            {
                cout << "\t" << bride << " dumped " << groom << " for " << suitor << "\n";
                bachelors.push(groom); 
                engaged[bride] = suitor; 
                break;
            }
        }
        bachelors.pop(); 
    }

    cout << "Engagements:\n";
    for (Couples::const_iterator it = engaged.begin(); it != engaged.end(); ++it)
    {
        cout << "\t" << it->first << " and " << it->second << "\n";
    }

    check_stability(engaged, men_pref, women_pref);

    cout << "Perturb:\n";
    std::swap(engaged["abi"], engaged["bea"]);
    cout << "\tengage abi with " << engaged["abi"] << " and bea with " << engaged["bea"] << "\n";

    check_stability(engaged, men_pref, women_pref);
}

Python: import copy

guyprefers = {
 'abe':  ['abi', 'eve', 'cath', 'ivy', 'jan', 'dee', 'fay', 'bea', 'hope', 'gay'],
 'bob':  ['cath', 'hope', 'abi', 'dee', 'eve', 'fay', 'bea', 'jan', 'ivy', 'gay'],
 'col':  ['hope', 'eve', 'abi', 'dee', 'bea', 'fay', 'ivy', 'gay', 'cath', 'jan'],
 'dan':  ['ivy', 'fay', 'dee', 'gay', 'hope', 'eve', 'jan', 'bea', 'cath', 'abi'],
 'ed':   ['jan', 'dee', 'bea', 'cath', 'fay', 'eve', 'abi', 'ivy', 'hope', 'gay'],
 'fred': ['bea', 'abi', 'dee', 'gay', 'eve', 'ivy', 'cath', 'jan', 'hope', 'fay'],
 'gav':  ['gay', 'eve', 'ivy', 'bea', 'cath', 'abi', 'dee', 'hope', 'jan', 'fay'],
 'hal':  ['abi', 'eve', 'hope', 'fay', 'ivy', 'cath', 'jan', 'bea', 'gay', 'dee'],
 'ian':  ['hope', 'cath', 'dee', 'gay', 'bea', 'abi', 'fay', 'ivy', 'jan', 'eve'],
 'jon':  ['abi', 'fay', 'jan', 'gay', 'eve', 'bea', 'dee', 'cath', 'ivy', 'hope']}
galprefers = {
 'abi':  ['bob', 'fred', 'jon', 'gav', 'ian', 'abe', 'dan', 'ed', 'col', 'hal'],
 'bea':  ['bob', 'abe', 'col', 'fred', 'gav', 'dan', 'ian', 'ed', 'jon', 'hal'],
 'cath': ['fred', 'bob', 'ed', 'gav', 'hal', 'col', 'ian', 'abe', 'dan', 'jon'],
 'dee':  ['fred', 'jon', 'col', 'abe', 'ian', 'hal', 'gav', 'dan', 'bob', 'ed'],
 'eve':  ['jon', 'hal', 'fred', 'dan', 'abe', 'gav', 'col', 'ed', 'ian', 'bob'],
 'fay':  ['bob', 'abe', 'ed', 'ian', 'jon', 'dan', 'fred', 'gav', 'col', 'hal'],
 'gay':  ['jon', 'gav', 'hal', 'fred', 'bob', 'abe', 'col', 'ed', 'dan', 'ian'],
 'hope': ['gav', 'jon', 'bob', 'abe', 'ian', 'dan', 'hal', 'ed', 'col', 'fred'],
 'ivy':  ['ian', 'col', 'hal', 'gav', 'fred', 'bob', 'abe', 'ed', 'jon', 'dan'],
 'jan':  ['ed', 'hal', 'gav', 'abe', 'bob', 'jon', 'col', 'ian', 'fred', 'dan']}

guys = sorted(guyprefers.keys())
gals = sorted(galprefers.keys())


def check(engaged):
    inverseengaged = dict((v,k) for k,v in engaged.items())
    for she, he in engaged.items():
        shelikes = galprefers[she]
        shelikesbetter = shelikes[:shelikes.index(he)]
        helikes = guyprefers[he]
        helikesbetter = helikes[:helikes.index(she)]
        for guy in shelikesbetter:
            guysgirl = inverseengaged[guy]
            guylikes = guyprefers[guy]
            if guylikes.index(guysgirl) > guylikes.index(she):
                print("%s and %s like each other better than "
                      "their present partners: %s and %s, respectively"
                      % (she, guy, he, guysgirl))
                return False
        for gal in helikesbetter:
            girlsguy = engaged[gal]
            gallikes = galprefers[gal]
            if gallikes.index(girlsguy) > gallikes.index(he):
                print("%s and %s like each other better than "
                      "their present partners: %s and %s, respectively"
                      % (he, gal, she, girlsguy))
                return False
    return True

def matchmaker():
    guysfree = guys[:]
    engaged  = {}
    guyprefers2 = copy.deepcopy(guyprefers)
    galprefers2 = copy.deepcopy(galprefers)
    while guysfree:
        guy = guysfree.pop(0)
        guyslist = guyprefers2[guy]
        gal = guyslist.pop(0)
        fiance = engaged.get(gal)
        if not fiance:
            
            engaged[gal] = guy
            print("  %s and %s" % (guy, gal))
        else:
            
            galslist = galprefers2[gal]
            if galslist.index(fiance) > galslist.index(guy):
                
                engaged[gal] = guy
                print("  %s dumped %s for %s" % (gal, fiance, guy))
                if guyprefers2[fiance]:
                    
                    guysfree.append(fiance)
            else:
                
                if guyslist:
                    
                    guysfree.append(guy)
    return engaged


print('\nEngagements:')
engaged = matchmaker()

print('\nCouples:')
print('  ' + ',\n  '.join('%s is engaged to %s' % couple
                          for couple in sorted(engaged.items())))
print()
print('Engagement stability check PASSED'
      if check(engaged) else 'Engagement stability check FAILED')

print('\n\nSwapping two fiances to introduce an error')
engaged[gals[0]], engaged[gals[1]] = engaged[gals[1]], engaged[gals[0]]
for gal in gals[:2]:
    print('  %s is now engaged to %s' % (gal, engaged[gal]))
print()
print('Engagement stability check PASSED'
      if check(engaged) else 'Engagement stability check FAILED')