[рони]

Sav2907,
шифровка из центра ...

var arr = [[257,],[257,258],[257,258],[258,257],[258,],[257,],[257,35],[257,35],[258,257],[258,257],[257,248],[248,257],[247,257]];
function fn(arr) {
    return arr.reduce(function(a, b, i, c) {
        var n = c[i - 1];
        return a += +(!i || b[1] !== void 0 && (!n.includes(b[0]) || !n.includes(b[1])))
    }, 0)
};

alert(fn(arr));

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