CODEWITHSUNDEEP
algorithmsequence
Larionov Nikita
Larionov Nikita

Reputation: 117

How to find subsequences of identical elements in an array

I am looking for an algorithm for my hobby task.

For example we have test data cases:

var case1 = ['green', 'red', 'red', 'blue', 'green', 'green', 'green'];
var case2 = ['blue', 'blue', 'green', 'yellow', 'blue', 'orange', 'green', 'green', 'green', 'green'];
var case3 = ['purple', 'blue', 'blue', 'blue', 'red'];

Output:

var result1 = ['red', 'red', 'green', 'green', 'green'];
var result2 = ['blue', 'blue', 'green', 'green', 'green', 'green'];
var result3 = ['blue', 'blue', 'blue'];

Can anybody tell me which algorithm I should use? The classic way with duplicates - not like I looking.

Upvotes: 0

Views: 63

Answers (2)

OmG3r
OmG3r

Reputation: 1811

Short version

we can use the .filter function to achieve this behavior.

.filter((item, i, array) => array[i - 1] == item || item == array[i + 1])


let case1 = ['green', 'red', 'red', 'blue', 'green', 'green', 'green'];
let case2 = ['blue', 'blue', 'green', 'yellow', 'blue', 'orange', 'green', 'green', 'green', 'green'];
let case3 = ['purple', 'blue', 'blue', 'blue', 'red'];

let result1 = case1.filter((item, i, array) => array[i - 1] == item || item == array[i + 1])
let result2 = case2.filter((item, i, array) => array[i - 1] == item || item == array[i + 1])
let result3 = case3.filter((item, i, array) => array[i - 1] == item || item == array[i + 1])

console.log(result1)
console.log(result2)
console.log(result3)

out of bounds index in javascript will return undefined which will evaluate to false in your comparison

Upvotes: 1

zaitsman
zaitsman

Reputation: 9499

So in javascript a naive implementation would be:

function selectSequential(source) {
   var result = [];
   for (let i = 0; i < source.length; i++) {
      if ((i != source.length-1 && source[i+1] === source[i]) 
            || (i != 0 && source[i-1] === source[i])) {
         result.push(source[i]);
      }
   }
   return result;
}

Upvotes: 1

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