Codility - Lesson 8 Leader - 2. Dominator

Source Link:
https://codility.com/programmers/lessons/8-leader/dominator/

Question:

A zero-indexed 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

 class Solution { public int solution(int[] A); }

 that, given a zero-indexed 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.

Assume that:

• 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].

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.

Complexity:

• expected worst-case time complexity is O(N);
• expected worst-case space complexity is O(1), beyond input storage (not counting the storage required for input arguments).

Elements of input arrays can be modified.

My Solution:
Notes:
1. Using "hashMap" for counting
Map<Integer, Integer> map = new HashMap<>(); 
2. Counting
// map(key, value) ---> map(number, count)
3. find the max number of counts
// note: use "map.keySet()" in for loop  
for( int key: map.keySet() ){
...
} 
4. check if there is a "dominator" or not
if( max_Count > (A.length)/2 ){
...
}
5. return "any index" of "the dominator"
if(A[i] == max_Number){
return i; // return the index
}