코딜리티 - Dominator (javascript)

Task description

 

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].

 

풀이

 

function solution(A) {
    const map = new Map();
    let answer = -1;

    A.forEach((v, i)=> {
        map.set(v, map.has(v) ? [map.get(v)[0] + 1, i] : [1, i]);
    })

    for(let v of map.values()) {
        if (v[0] > Math.floor(A.length / 2)) answer = v[1];
    }

    return answer;
}