코딩테스트#014 MaxProductOfThree

문제

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:

class Solution { public int solution(int[] 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].

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나의 풀이

import java.util.*;

class Solution {
    public int solution(int[] A) {
        
        Arrays.sort(A);

        int i = A.length;

        int num = A[i - 1] * A[i - 2] * A[i - 3];
        
        int num2 = 0;
        if (A[0] < 0 && A[1] < 0) {
            num2 = A[0] * A[1] * A[i - 1];
        }

        return (num > num2)? num : num2;
    }
}

check 1 : sorting + 음수의 곱인 경우