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MaxProductOfThree (Lesson 6)

Instructions​

A non-empty array A consisting of N integers is given. The product of triplet (P, Q, R) equates to A[P] _ A[Q] _ A[R] (0 ≤ P < Q < R < N).

For example, array A such that:

A[0] = -3
A[1] = 1
A[2] = 2
A[3] = -2
A[4] = 5
A[5] = 6

contains the following example triplets:

  • (0, 1, 2), product is −3 _ 1 _ 2 = −6
  • (1, 2, 4), product is 1 _ 2 _ 5 = 10
  • (2, 4, 5), product is 2 _ 5 _ 6 = 60

Your goal is to find the maximal product of any triplet.

Write a function:

function solution(A);

that, given a non-empty array A, returns the value of the maximal product of any triplet.

For example, given array A such that:

A[0] = -3
A[1] = 1
A[2] = 2
A[3] = -2
A[4] = 5
A[5] = 6

the function should return 60, as the product of triplet (2, 4, 5) is maximal.

Write an efficient algorithm for the following assumptions:

  • N is an integer within the range [3..100,000];
  • each element of array A is an integer within the range [−1,000..1,000].

Translate to Korean​

배열에서 3개의 수를 곱해서 나올 수 있는 가장 큰 값을 구하면 된다.

Solution​

function solution(A) {
  const sortList = [...A].sort((a, b) => a - b);
  const lastIdx = sortList.length - 1;

  return Math.max(
    sortList[0] * sortList[1] * sortList[lastIdx],
    sortList[lastIdx] * sortList[lastIdx - 1] * sortList[lastIdx - 2]
  );
}

Review​

sort를 해준 뒤 나오는 가장 큰 3개의 값을 곲하면 가장 큰 수가 나온다. (이하 standardMaxNum)

-> 하지만 음수 2개 + 양수 1개를 했을 경우 standardMaxNum 보다 큰 값이 나올 수도 있다.

References​