meetings.js

function getTimeslots(meetings) {
    sortMeetings(meetings);
    meetings = removeContained(meetings);

    var timeslots = [], current, next;
    for (var i = 0; i < meetings.length - 1; i++) {
        current = meetings[i];
        next = meetings[i + 1];

        if (current[1] < next[0]) {
            timeslots.push([current[1], next[0]]);
        }
    }
    return timeslots;
}

function sortMeetings(meetings) {
    meetings.sort(function (a, b) {
        if (a[0] < b[0]) {
            return -1;
        } else if (a[0] > b[0]) {
            return 1;
        } else {
            if (a[1] < b[1]) {
                return -1;
            } else {
                return 1;
            }
        }
    });
}

function removeContained(input) {
    var meetings = [], current, previous;

    if (input.length > 0) {
        for (var i = input.length - 1; i > 0; i--) {
            current = input[i];
            previous = input[i - 1];
            if (current[1] < previous[1]) {
                continue;
            }
            meetings.unshift(current);
        }
        meetings.unshift(input[0]);
    }

    return meetings
}

var tests = {total: 0, passed: 0, failed: 0};

function check(meetings, expected) {
    tests.total++;

    var timeslots = getTimeslots(meetings);
    if (timeslots.toString() == expected.toString()) {
        tests.passed++;
    } else {
        tests.failed++;
        console.error("Expected: " + JSON.stringify(expected) + ". Got: " + JSON.stringify(timeslots));
    }
}

check(
    [[0, 1], [3, 5], [4, 8], [10, 12], [4, 7], [9, 10]],
    [[1, 3], [8, 9]]
);

check(
    [[0, 1], [1, 12]],
    []
);

check(
    [],
    []
);

check(
    [[1, 3]],
    []
);

check(
    [[3, 5], [2, 6], [7, 10]],
    [[6, 7]]
);

console.log(tests);