Finding the greatest amount of consecutive values in an array (JS)

Question

I'm trying to solve a problem that I can't seem to wrap my head around and was hoping I could get a little bit of insight from someone more experienced than I am. Basically, I have an array that has anywhere from 10 to 500 values. These values are all either true or false, but they are in a random order. I need to know the greatest amount of times that false appears in a row. For example:

[false, false, true, false, true, false, true, false, false, false]

Should return 3, since it appears 3 times in a row at the most. This seems like a potentially common problem to solve but I couldn't find a solution through searching. Any help would be greatly appreciated!

What have you tried? If you're stuck - how would you solve it by hand? That's usually a good starting point. — Damon
– Damon, Commented Jun 6, 2017 at 22:29

Nenad Vracar · Accepted Answer · 2017-06-06 22:33:01Z

9

You can use one value to keep count of consecutive false values and if that value is larger then current max set max value to that value. If value is true you reset counter to 0.

var arr = [false, false, true, false, true, false, true, false, false, false]
var c = 0, max = 0;

arr.forEach(function(e) {
  e == false ? c++ : c = 0;
  if (c > max) max = c;
})

console.log(max)

answered Jun 6, 2017 at 22:33

Nenad Vracar

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2 Comments

Aidan Vanleuven Over a year ago

This makes a lot of sense, seems like the answer was right under my nose the whole time. Very much appreciated!

Nenad Vracar Over a year ago

Glad i could help.

BenM · Accepted Answer · 2017-06-06 22:36:39Z

1

You could simply use the forEach function, and then have an internal counter, for example:

console.log( countConsecutive([false, false, true, false, true, false, true, false, false, false]) );

function countConsecutive( arr )
{
   var c = 0;
  
   arr.forEach(function(e) {  
     (e == false) ? c++ : c = 0;
  });
  
  return c;
}

answered Jun 6, 2017 at 22:36

BenM

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Comments

Oghli · Accepted Answer · 2017-06-06 23:03:50Z

1

Try this function to count number of consecutive false in array:

function countNumFalse(arr){
    var max = 0;
    var condFalse = false;
    var numFalse = 0;
    for (var i = 0; i < arr.length; i++) {
        condFalse = condFalse || arr[i];
        if(condFalse === true){
           condFalse = false;
           numFalse = 0;
        }
        else{
             numFalse++;
          if(numFalse > max){
             max = numFalse;
          }
        }
    }
    return max;
}

var arr1 = [false, false, true, false, true, false, true, false, false, false];

countNumFalse(arr1);
3

edited Jun 6, 2017 at 23:03

answered Jun 6, 2017 at 22:55

Oghli

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Comments

Chris Thornton · Accepted Answer · 2017-06-06 22:34:37Z

0

var yourArray=[false,true,true,false,false,false,true];
arrayLength = yourArray.length;
var maxCount=0;
var currentCount=0;
var lastElement;

for(var i = 0;i<arrayLength;i++){
    if(lastElement === yourArray[i]){
        currentCount++;
    }
    else{
        if(currentCount>maxCount){
            maxCount=currentCount;
        }
        currentCount=1;
    }
    lastElement=yourArray[i];
}
console.log(maxCount);

This should suit your needs

answered Jun 6, 2017 at 22:34

Chris Thornton

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Comments

elPastor · Accepted Answer · 2019-03-09 05:08:21Z

0

Here's a funky, but one-lined solution:

var arr = [false, false, false, true, false, false, true, false, false, true];

var consec = arr.join('').split('true').reduce((i, x) => Math.max((x.match(/false/g) || []).length, i), 0);

Steps explained:

Convert the array to a string
Split the new string on the values we don't want to create an array of each of the consecutive items in string form.
Then reduce that array and within the reduce function, count the number of matches via a regex match - and find the maximum number of those matches.

Point of note - this really only works with binary lists [true, false], [1,0], etc.

Fiddle.

answered Mar 9, 2019 at 5:08

elPastor

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