MaxProductOfThree

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:

    int solution(vector<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].

#include <algorithm>

int solution(vector<int> &A) {
    // write your code in C++11 (g++ 4.8.2)
    sort(A.begin(), A.end());
    
    int s = int(A.size());
    
    int m1 = A[s - 1] * A[s- 2] * A[s - 3];
    if ((A[s - 1] < 0) || (A[0] > 0)) return m1;
    
    int m2 = A[0] * A[1] * A[s- 1];
    
    return max(m1, m2);
}