From 283f805ef24a974e61a6548f1974ba7a3770522c Mon Sep 17 00:00:00 2001
From: s50600822 <s50600822@gmail.com>
Date: Sun, 26 Nov 2023 03:20:16 +1100
Subject: [PATCH] https://leetcode.com/problems/maximum-product-subarray impl

---
 .../maximum_product_subarray/Solution.java    | 27 +++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/interview_prep/algorithm/java/ide_handicapped/maximum_product_subarray/Solution.java b/interview_prep/algorithm/java/ide_handicapped/maximum_product_subarray/Solution.java
index 69f3ede..aa42f13 100644
--- a/interview_prep/algorithm/java/ide_handicapped/maximum_product_subarray/Solution.java
+++ b/interview_prep/algorithm/java/ide_handicapped/maximum_product_subarray/Solution.java
@@ -4,12 +4,35 @@
 
 class Solution {
     public int maxProduct(int[] n) {
-        return 99999;
+        int answer = n[0]; //just to start
+        int min = 1, max = 1;
+
+        for(int i=0; i<n.length; i++){
+            if(n[i] == 0){
+                // reset
+                min = 1;
+                max = 1;
+                // keep the answer unless neg
+                answer = Math.max(answer, n[i]);
+                continue;
+            }
+            //each step we have the choice between
+            //the value itself - fresh start
+            //the product with accumulated max
+            //the product with accumulated min - min negative could flip to max
+            int tmp = min;
+            min = Math.min(n[i], Math.min(min * n[i], max * n[i]));
+            max = Math.max(n[i], Math.max(tmp * n[i], max * n[i]));
+            answer = Math.max(answer, max);
+        }
+        return answer;
     }
+
     public static void main(String[] args) {
         //https://leetcode.com/problems/maximum-product-subarray/
         final Solution self = new Solution();
         assert self.maxProduct(new int[]{2,3,-2,4})==6;
-        assert self.maxProduct(new int[]{2,0,-1})==0;
+        assert self.maxProduct(new int[]{2,0,-1})==2;
+        assert self.maxProduct(new int[]{-2,0,-1})==0;
     }
 }
\ No newline at end of file