Find the maximum contiguous subsequence product -- InMobi

Problem

Suppose you have an array of +ve numbers, -ve numbers and zeroes. Devise an algorithm to find the maximum contiguous subsequence product. 

For 7 -3 -1 2 -40 0 3 6, the max subsequence product = -1 * 2 * -40 = 80 

For -3 7 2 0 -5 7 -2 -2 2, the maximum subsequence product = -5 * 7 * -2 = 70

Solution

This is exhaustive method.

Find the product of all possible sub sequences, and select the max one.

#include <iostream>

#include <iomanip>

#include <iterator>

#include <algorithm>

using namespace std;

int CalcProd(int* arr, int len)

{

    int prod = 1;

    for(int i = 0; i < len; i++){

        prod *= arr[i];

    }

    return prod;

}

int FindMaxSubSeqProduct(int* arr, int len)

{

    int maxProd = 1;

    int prod;

    for(int i = 1; i < len + 1; ++i){

        for(int j = 0; j < len - i + 1; ++j){

            prod = CalcProd(arr + j, i);

            if(prod > maxProd){

                maxProd = prod;

            }

        }

    }

    return maxProd;

}

int main(int argc, char* argv[])

{

    int testCases[][10] = {

        {-1, 0, 1},

        {1, -1, 0},

        {0, -1, 1},

        {7, -3, -1, 2, -40, 0, 3, 6},

        {-3, 7, 2, 0, -5, 7, -2, -2, 2},

        {0, 2, -2, -2, 3},

        {-3, -2, 3, -3, -4, -5, -6, -7},

        {-20, 10000, -20, 1}

    };

  

    int testCaseLens[] = {3, 3, 3, 8, 9, 5, 8, 4};

    for(int i = 0; i < sizeof(testCases)/sizeof(testCases[0]); ++ i){

        cout << "Test case " << i << endl;

        copy(testCases[i], testCases[i] + testCaseLens[i],

            ostream_iterator<int>(cout, "  "));

        cout << endl << "Max product is ";

        cout << FindMaxSubSeqProduct(testCases[i], testCaseLens[i]) 

            << endl << endl;

    }

    return 0;

}

Output

Test case 0

-1  0  1

Max product is 1

Test case 1

1  -1  0

Max product is 1

Test case 2

0  -1  1

Max product is 1

Test case 3

7  -3  -1  2  -40  0  3  6

Max product is 80

Test case 4

-3  7  2  0  -5  7  -2  -2  2

Max product is 70

Test case 5

0  2  -2  -2  3

Max product is 24

Test case 6

-3  -2  3  -3  -4  -5  -6  -7

Max product is 15120

Test case 7

-20  10000  -20  1

Max product is 4000000

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