Score 100/100

find-dominator-number.js

// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');

function solution(A) {
  // write your code in JavaScript (Node.js 8.9.4)
  let total = A.length;
  let occurences = {}
  let indexes = [];
  
  for (let i = 0; i < A.length; i++) {
      let elm = A[i]
      if (!occurences[elm]) {
          occurences[elm] = {
            count: 0,
            indexes: [],
          }
      }
      occurences[elm].count += 1;
      occurences[elm].indexes.push(i);
  }
  
  let dominator = Object.keys(occurences).find(idx => {
      return occurences[idx].count > (total/2)
  })
  
//   console.log(occurences[dominator].indexes)
  return dominator ? occurences[dominator].indexes[0] : -1
}


/*
An array A consisting of N integers is given. The dominator of array A is the value that occurs in more than half of the elements of A.

For example, consider array A such that

 A[0] = 3    A[1] = 4    A[2] =  3
 A[3] = 2    A[4] = 3    A[5] = -1
 A[6] = 3    A[7] = 3
The dominator of A is 3 because it occurs in 5 out of 8 elements of A (namely in those with indices 0, 2, 4, 6 and 7) and 5 is more than a half of 8.

Write a function

function solution(A);

that, given an array A consisting of N integers, returns index of any element of array A in which the dominator of A occurs. The function should return −1 if array A does not have a dominator.

For example, given array A such that

 A[0] = 3    A[1] = 4    A[2] =  3
 A[3] = 2    A[4] = 3    A[5] = -1
 A[6] = 3    A[7] = 3
the function may return 0, 2, 4, 6 or 7, as explained above.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [0..100,000];
each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
*/