Dgdrxrt

The task:

Given a list of elements, find the majority element, which appears
more than half the time (> floor(len(lst) / 2.0)).

You can assume that such element exists.

For example, given [1, 2, 1, 1, 3, 4, 0], return 1.

My solution:

const lst = [1, 2, 1, 1, 3, 4, 0];
const findMajorityElem = lst => lst.reduce((acc, x) => acc.major[1] < acc[x]) acc.major = [x, acc[x]]; 
 return acc;
, major: null).major[0];

console.log(findMajorityElem(lst));

If it is known that a majority element exists, then the efficient algorithm to use is the Boyer-Moore majority vote algorithm, which requires only O(1) space.

@200_success's suggestion seems like the right play here.

That said, I thought it was worth pointing out a couple small improvements to your approach:

• 
  major need only be the element itself (since you can look up its value in the accumulator)


• Since you tagged this functional-programming, you can use expressions everywhere, and avoid the if statement.

Revised code:

const findMajorityElem = lst => lst.reduce((acc, x) => , major: null).major

And just for fun, again based on your tag, here's a single-expression solution in Ramda. Again, I don't recommend actually using this given that Boyer-Moore exists:

pipe(
 groupBy(identity), 
 map(length), 
 toPairs, 
 converge( reduce(maxBy(last)), [head, identity] ),
 head, 
 parseInt
)(lst)

You can try it here

If the number exists, it should be done like this and shorter.

let result =
 [2,3,4,5,1,1,1,2,2,22,2,2,2,2,2,2,2,2,1,1,33,3,2,1,1,1,1,2,2,2,2,2].reduce( (a ,b) => 
 console.log(a)
return a.length == null ? ( a != b ? [] : a.concat(b)):
 a.length == 0 ? [b] :
 a[a.length-1] == b ? a.concat(b) :
 a.slice(0,a.length-2) ;
 )[0]

 console.log(result) //2