Question

I Implemented the Kadane’s Max Sub array problem in javascript but seems i end up always getting 0 in the console even though there exists higher numbers( I understand that it does what it’s doing because of for loop from 0 - size where size = subarray size).

• So how do i implement the algorithm correctly?

• Does it also work for all positive integer array?

JsBin

http://jsbin.com/ajivan/edit#javascript,live

Answer 1

You’re passing n=3 as an argument while your array has length 6. I changed your algorithm to use length:

function SubSequence(a){
  var now = 0,prev =0;
  for(var i = 0;i < a.length;i++){  
    prev = Math.max(0,prev + a[i]);
    now = Math.max(prev,now);
  }
  return now;
}

console.log(SubSequence([-1,-2,-3,4,6,7]));

and it gives 17.

Does it also work for all positive integer array?

Yes, it will then give sum of all elements in the array.

---

If you want maximal subsequence of length 3, use

function SubSequence(a,n){
  var now = 0;
  for(var i = 0; i < n; i++) {
    now += a[i];
  }
  var best = now;
  for(var i = n;i < a.length;i++) {
    now += a[i] - a[i-n];
    best = Math.max(now,best);
  }
  return best;
}

console.log(SubSequence([-1,-2,-3,4,6,7,1,4],3));

the best is 4+6+7, while 4+6+7+1+4 is not allowed.