Check if at least two out of three booleans are true

Question

An interviewer recently asked me this question: given three boolean variables, a, b, and c, return true if at least two out of the three are true.

My solution follow

Answer 1

Here's another implementation using map/reduce. This scales well to billions of booleans^© in a distributed environment. Using MongoDB:

Creating a database values of booleans:

db.values.insert({value: true});
db.values.insert({value: false});
db.values.insert({value: true});

Creating the map, reduce functions:

Edit: I like CurtainDog's answer about having map/reduce apply to generic lists, so here goes a map function which takes a callback that determines whether a value should be counted or not.

var mapper = function(shouldInclude) {
    return function() {
        emit(null, shouldInclude(this) ? 1 : 0);
    };
}

var reducer = function(key, values) {
    var sum = 0;
    for(var i = 0; i < values.length; i++) {
        sum += values[i];
    }
    return sum;
}

Running map/reduce:

var result = db.values.mapReduce(mapper(isTrue), reducer).result;

containsMinimum(2, result); // true
containsMinimum(1, result); // false


function isTrue(object) {
    return object.value == true;
}

function containsMinimum(count, resultDoc) {
    var record = db[resultDoc].find().next();
    return record.value >= count;
}