[рони]

Panwo,

var a = [
    [1, 2, 3, 3, 4],
    [, , 3, 3, ],
    [, 1, 3, 3, ],
    [, , 3, 3, ],
    [5, , 3, 3, ]
];

function getLetters(a) {
    var letters = new Array();
    var i, j;
    Array.prototype.hasObject = (!Array.indexOf ? function(o) {
        var l = this.length + 1;
        while (l -= 1) {
            if (this[l - 1] === o) return true;
        }
        return false;
    } : function(o) {
        return (this.indexOf(o) !== -1);
    });
    for (i = 0; i < 5; i++) {
        for (j = 0; j < 5; j++) {
            if (a[i][j] && !letters.hasObject(a[i][j])) {
                letters.push(a[i][j]);
            }
        }
    }
    return letters;
}
alert(getLetters(a))