Matt Tarbit's Weblog

A minor morsel

I haven't posted in ages, so I might as well use this to break radio silence. It's a solution to this little programming brain teaser from Dustin Diaz. I don't think it's as much of a puzzle as he seemed think, given by the responses in the comments and how long it took me, but regardless:

var listA = ['a', 'b', 'c', 'c', 'd', 'e', 'e', 'e', 'e', 'e', 'f', 'e', 'f', 'e', 'f', 'a', 'a', 'a', 'f', 'f', 'f'];
var listB = [];

var count = 0;

listA.forEach(function(val,key,arr){
    var matchPrev = (val == arr[key - 1]);
    var matchNext = (val == arr[key + 1]);

    count = matchPrev ? count+1 : 0;

    if (count == 2) {
        val = '<span>' + val;
    }
    if (count >= 2 && !matchNext) {
        val += '</span>';
    }

    listB.push(val);
});

console.log(listB.join(' '));

As some of the commenters' solutions show, it can be done in a one-line regular expression, but I was sticking to the "rules" implicit in the original post.

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