[рони]

Blondinka,
вариант для 3

<script>
var arr = [9, 9, 9, 111, 5, 2, 5, 3, 4, 4, 5, 7] ;

function test(a) {
    a = a.slice().sort(function(a, b) {
        return a - b
    });
    return a.some(function(c, b) {
        var d = a[b + 1],
            e = a[b + 2];
        return c == d - 1 && c == e - 2 && (a = [c, d, e])
    }) && a
};
document.write(JSON.stringify(test(arr)))
  </script>