dsalgo/MaxProductSubArray.java at master · gnedster/dsalgo · GitHub

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/*
For problem and solution description please visit the link below
http://www.dsalgo.com/2013/02/maximum-product-subarray.html
*/

package com.dsalgo;


public class MaxProductSubArray
{
 public static void main(String[] args)
 {
  int[] arr =
  { 1, 2, -1, 4, 0, 5, -6, -5, -6, 2, 0, 3, -4, 3, -2, 4, -3 };
  int[] returnIndices = new int[2];
  long maxProduct = findMaxProduct(arr, returnIndices);
  System.out.println("Maximum product " + maxProduct);
  System.out.println("Indices " + returnIndices[0] + " - "
    + returnIndices[1]);
 }

 private static long findMaxProduct(int[] arr, int[] returnIndices)
 {
  int startIndex = 0;
  long maxProduct = 0;
  int[] indices = new int[2];
  for (int index = 0; index < arr.length; ++index)
  {
   if (arr[index] == 0 && index >= startIndex)
   {
    long product = findMaxProductWithoutZero(arr, startIndex,
      index - 1, indices);
    if (product > maxProduct)
    {
     maxProduct = product;
     returnIndices[0] = indices[0];
     returnIndices[1] = indices[1];
    }
    startIndex = index + 1;
   } else if (index == arr.length - 1)
   {
    long product = findMaxProductWithoutZero(arr, startIndex, index,
      indices);
    if (product > maxProduct)
    {
     maxProduct = product;
     returnIndices[0] = indices[0];
     returnIndices[1] = indices[1];
    }
   }
  }
  return maxProduct;
 }

 private static long findMaxProductWithoutZero(int[] arr, int startIndex,
   int endIndex, int[] returnIndices)
 {
  if (startIndex > endIndex || startIndex < 0 || endIndex >= arr.length)
   return 0;
  int negativeCount = 0;
  int firstNegativeIndex = -1;
  int lastNegativeIndex = -1;
  for (int index = startIndex; index <= endIndex; ++index)
  {
   if (arr[index] < 0)
   {
    negativeCount++;
    if (firstNegativeIndex == -1)
     firstNegativeIndex = index;
    lastNegativeIndex = index;
   }
  }
  if (negativeCount % 2 == 0)
   return findMaxProductWithoutNegative(arr, startIndex, endIndex,
     returnIndices);
  else
  {
   int[] indices = new int[2];
   long maxProduct = findMaxProductWithoutNegative(arr,
     firstNegativeIndex + 1, endIndex, indices);
   returnIndices[0] = indices[0];
   returnIndices[1] = indices[1];
   long maxProduct2 = findMaxProductWithoutNegative(arr, startIndex,
     lastNegativeIndex - 1, indices);
   if (maxProduct2 > maxProduct)
   {
    maxProduct = maxProduct2;
    returnIndices[0] = indices[0];
    returnIndices[1] = indices[1];
   }
   return maxProduct;
  }
 }

 private static long findMaxProductWithoutNegative(int[] arr,
   int startIndex, int endIndex, int[] indices)
 {
  if (startIndex > endIndex || startIndex < 0 || endIndex >= arr.length)
   return 0;
  long product = 1;
  for (int index = startIndex; index <= endIndex; ++index)
   product *= arr[index];
  indices[0] = startIndex;
  indices[1] = endIndex;
  return product;
 }
}