Question 176818 in Javascript Question posted in
A very good W3school tutorial can be found here.

Does Javascript have a sequence of equal numbers in an array?

I want to push the first sequence to currentSequence, then store it in maxSequence, then push the next sequence in currentSequence, check if its length is greater, if it isn’t proceed further, if it is store it in maxSequence. I’d like to keep the original order of the array.

 let arr = ['2','1','1','2','3','3','2','2','2','1'].map(Number)

let maxSequence = []

for(let i = 0; i< arr.length; i++){
     let currentSequence = []
  if( arr[i] === arr[i+1] ){ 
    currentSequence.push(arr[i]);
  //currentSequence = arr.toSpliced(i, 1);
  }
  if(currentSequence.length > maxSequence.length){
      maxSequence = currentSequence  
  }
  }
   console.log(maxSequence.length) // expected output: 3
   console.log(maxSequence) // expected output: [2, 2, 2]
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3

Answers


  1. 0

    This can be achieved like so:

    let arr = ['2', '1', '1', '2', '3', '3', '2', '2', '2', '1'].map(Number)

let maxSequence = [];
let currentSequence = [];
let currentValue = -1;

for (let i = 0; i < arr.length; i++) {
  if (arr[i] === currentValue) {
    currentSequence.push(arr[i]);
  } else {
    currentValue = arr[i];
    currentSequence = [currentValue];
  }
  if (currentSequence.length > maxSequence.length) {
    maxSequence = currentSequence
  }
}
console.log(maxSequence.length) // expected output: 3
console.log(maxSequence) // expected output: [2, 2, 2]
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  2. 0

    One way of doing what you need is:

    let arr = ["2", "1", "1", "2", "3", "3", "2", "2", "2", "1"].map(Number);

let maxSequence = [];
let currentSequence = [arr[0]];

for (let i = 1; i < arr.length; i++) {
  if (arr[i] !== arr[i - 1]) { // if current number does not match the one before it
    if (currentSequence.length > maxSequence.length) { // it means currentSequence is complete and we need to check if it's larger than current maxSequence or not
      maxSequence = currentSequence;
    }
    currentSequence = [arr[i]]; // then need to reset the currentSequence array
    continue;
  }
  currentSequence.push(arr[i]); // else if numbers match, we push current number to the currentSequence
}
console.log(maxSequence.length); // expected output: 3
console.log(maxSequence); // expected output: [2, 2, 2]
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  3. 0

    Can be done without an intermediate array.

    let arr = ['2','1','1','2','3','3','2','2','2','1'].map(Number);
let maxSequence;

(() => {
    let maxRunVal = arr[0], maxRun = 1;
    for (let i = 1, run = 1; i < arr.length; i++) {
        if (arr[i] == arr[i-1]) {
            run++;
            if (run > maxRun) {
                maxRun = run;
                maxRunVal = arr[i];
            }
        }
        else {
            run = 1;
        }
    }
    maxSequence = new Array(maxRun);
    maxSequence.fill(maxRunVal);
})();

console.log(maxSequence.length);
console.log(maxSequence);
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