find the repeated sequences of characters within the text

Question

find the repeated sequences of characters within the text

Trying to grasp a javascript string variable source;

Is there an efficient technique to identify all REPEATED substrings of length around 20 characters (even if they overlap or include substrings of slightly different lengths)?

An approach that could be considered is:

var len=20;
var sourceLen=source.length;
for (var i=0; i<sourceLen; i++){
    for (var j=i+1; j<sourceLen; j++){
        if (source.substring(i,i+len)==source.substring(j,j+len)){
            console.log(source.substring(i,i+len));
        }
    }
}

However, as the string size increases, the computation time also escalates significantly. There's been pondering about adjusting the steps of value exchanging (j+=5; instead of j++), but encountered certain constraints.

Another idea has been to explore using .indexOf to achieve similar outcomes with just one for-loop.

Are there any smarter strategies available to extract a list of duplicated strings of approximately 20 characters within the given string?

javascript string performance loops substring

Answer 1

Answer №1

I was contemplating the use of .indexOf in order to achieve similar results with a single for-loop.

indexOf actually internally loops through the string. It's uncertain if they have integrated a more efficient string search algorithm; it might be worth experimenting with.

Is there a more clever approach to extract a list of duplicate strings that are exactly 20 characters long from the given string?

One could utilize a set containing all substrings for quick lookup.

function findDuplicates(input, length, callback) {
    var subStrings = {};
    for (var i=0; l=input.length-length; i<l; i++) {
        var sub = input.slice(i, length);
        if (sub in subStrings) // or even better: subStrings[sub]===true
            callback(sub);
        else
            subStrings[sub] = true;
    }
}
findDuplicates("…", 20, console.log.bind(console));

Answer 2

I was contemplating the use of .indexOf in order to achieve similar results with a single for-loop.

indexOf actually internally loops through the string. It's uncertain if they have integrated a more efficient string search algorithm; it might be worth experimenting with.

Is there a more clever approach to extract a list of duplicate strings that are exactly 20 characters long from the given string?

One could utilize a set containing all substrings for quick lookup.

function findDuplicates(input, length, callback) {
    var subStrings = {};
    for (var i=0; l=input.length-length; i<l; i++) {
        var sub = input.slice(i, length);
        if (sub in subStrings) // or even better: subStrings[sub]===true
            callback(sub);
        else
            subStrings[sub] = true;
    }
}
findDuplicates("…", 20, console.log.bind(console));

find the repeated sequences of characters within the text

Answer №1

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