Maximum Product Subarray

Given a nonempty integer array nums, return the largest product obtainable by multiplying every element in one nonempty contiguous subarray.
A contiguous subarray uses consecutive elements of nums. You may choose a single element, and the array may contain negative numbers and zeros.
Return the product value, rather than the chosen subarray or its indices. Products are exact signed integers; do not apply a modulus.

Function
maxProduct(nums: int[]) → long

Examples
Example 1
nums = [2,3,-2,4]
return = 6
The subarray [2,3] has product 6. Any subarray containing -2 has a negative product, and the remaining singleton [4] has product 4.
Example 2
nums = [-2,3,-4]
return = 24
The entire array is contiguous, and its product is (-2) * 3 * (-4) = 24. The two negative factors produce a positive product.
Example 3
nums = [-2,0,-1]
return = 0
The singleton [0] has product 0, larger than either negative singleton. The values -2 and -1 cannot be multiplied together without including the intervening zero.

Constraints
1 <= nums.length <= 10^5.
-10 <= nums[i] <= 10.
The product of every nonempty contiguous subarray is guaranteed to lie between -10^18 and 10^18, inclusive.
The returned value must use a signed 64-bit integer or a wider exact integer type.

The trick: track both the maximum and the minimum product ending at the current index. A negative number flips them, so the most negative product can become the largest after one more negative multiplication. At each element x, compute candidates x, curMax*x, curMin*x. New max is the biggest, new min is the smallest. Update the global answer with the max. Zeros reset things automatically because x itself is a candidate, which is why [-2,0,-1] returns 0. The common pitfall is tracking only the max, which gives 6 instead of 24 on Example 2. Another is overwriting curMax before computing curMin, so use a temp variable. It's O(n) time and O(1) space. Use a 64-bit integer since products reach 10^18. If the swap logic slips under pressure, StealthCoder is the hedge for the live OA, giving you the working code when your head goes blank.

Memorize the pattern. If you can't, run StealthCoder. The proctor sees the IDE. They don't see what's behind it.