참조 : https://medium.com/@aliasav/algorithms-maximum-product-subarray-b09e520b4baf
참조 : https://leetcode.com/problems/maximum-product-subarray/discuss/1608747/Daily-LeetCoding-Challenge-December-Day-3/1169035
관련 문제 : LeetCode No.152 (https://leetcode.com/problems/maximum-product-subarray/)