Leetcode–Maximum Product Subarray

The Problem:

Find the contiguous subarray within an array (containing at least one number) which has the largest product.

For example, given the array [2,3,-2,4],
the contiguous subarray [2,3] has the largest product = 6.


  1. Keep track of a minAt and a maxAt of product ending with each index. The trick is to record minAt, it covers the case that previously has a negative number (we discarded in maxAt), but later have another negative number which together may result in a bigger product.
  2. minAt and maxAt should be updated after all computed, so use a temp variable to hold first.

Java Solution

public class Solution {
    public int maxProduct(int[] A) {
        int maxAt = A[0];
        int minAt = A[0];
        int max = A[0];
        int tempMax, tempMin;
        for(int i = 1; i < A.length; i++){
            tempMax = Math.max(Math.max(maxAt * A[i], minAt * A[i]), A[i]);
            tempMin = Math.min(Math.min(maxAt * A[i], minAt * A[i]), A[i]);
            maxAt = tempMax;
            minAt = tempMin;
            max = Math.max(maxAt, max);
        return max;

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