How do I optimise this javascript function for speed? -

i took codility tape equilibrium test here

as can see score didn't enough on how fast function executes. can give me pointers can optimise code , closer 100%?

here code...

function solution(a) {      var minimumabsdiff = null;      for(var currentindex =1;currentindex < a.length;currentindex ++){         var bottomhalf = gettotal(0,currentindex-1,a);         var tophalf = gettotal(currentindex,a.length-1,a);           var absdiff = math.abs(bottomhalf - tophalf);          if(minimumabsdiff == null){             minimumabsdiff = absdiff;          }else{             if(absdiff < minimumabsdiff) minimumabsdiff = absdiff;          }      }      return minimumabsdiff; }  function gettotal(start,end,arraytocheck){     var total = 0;     for(var currentindex = start;currentindex <= end;currentindex++){         total = total + arraytocheck[currentindex];     }     return total; } 

you don't want optimise speed. want lower algorithmic complexity. current algorithm o(n²), while taks description explicitly stated that

• expected worst-case time complexity o(n);
• expected worst-case space complexity o(n), beyond input storage (not counting storage required input arguments).

so what's insight make possible? each total difference small distance others p. if compare value |(a[0] + ... + a[p-1]) - (a[p] + ... + a[n-1])| p , p+1, there constant amount of work difference done.

function solution(a) {      var left = 0,          right = a.reduce(function(a, b) { return + b; }, 0);      var min = infinity;      (var p = 0; p<a.length-1; p++) {          left += a[p];          right -= a[p];          min = math.min(min, math.abs(left - right));      }      return min; }