impl max product subarray

leetcode-cc/MaxProductSubarray.hpp

@@ -1,3 +1,5 @@
+#include <algorithm>
+
 #include "TestHelper.h"
 #include "problem.h"
 #include "solution.h"
@@ -8,7 +10,7 @@ IMPLEMENT_PROBLEM_CLASS(PMaxProductSubarray, 152, DIFFI_MEDIUM,
                         TOPIC_ALGORITHMS, "Maximum Product Subarray",
                         "Given an integer array nums, find a subarray that has "
                         "the largest product, and return the product.",
-                        {""});
+                        {"DP"});
 
 class SMaxProductSubarray : public ISolution {
  public:
@@ -18,12 +20,52 @@ class SMaxProductSubarray : public ISolution {
   }
   string location() const override { return __FILE_NAME__; }
   int test() const override {
-    return testHelper<vector<int>, int>(
-        {{2, 3, -2, 4}, {-2, 0, -1}}, {6, 0},
-        [this](auto input) { return this->maxProduct(input); });
+    return testHelper<vector<int>, int>({{2, 3, -2, 4}, {-2, 0, -1}}, {6, 0},
+                                        [this](auto input) {
+                                          // return this->maxProduct(input);
+                                          return this->maxProductV2(input);
+                                        });
   };
   int benchmark() const override { return 0; }
 
  private:
-  int maxProduct(vector<int>& nums) const {}
+  // work, but time limit
+  int maxProduct(vector<int>& nums) const {
+    int n = nums.size();
+    vector<vector<int>> dp(n, vector(n, 0));
+    int res = INT_MIN;
+
+    for (int i = 0; i < n; i++) {
+      dp[i][i] = nums[i];
+      res = max(res, dp[i][i]);
+    }
+
+    for (int i = 0; i < n; i++) {
+      for (int j = i + 1; j < n; j++) {
+        dp[i][j] = dp[i][j - 1] * nums[j];
+        res = max(res, dp[i][j]);
+      }
+    }
+
+    return res;
+  }
+
+  int maxProductV2(vector<int>& nums) const {
+    int n = nums.size();
+    if (n == 0) return 0;
+
+    int max_product = nums[0];
+    int min_product = nums[0];
+    int result = nums[0];
+
+    for (int i = 1; i < n; ++i) {
+      int temp_max = max_product;
+      int temp_min = min_product;
+      max_product = max({nums[i], nums[i] * temp_max, nums[i] * temp_min});
+      min_product = min({nums[i], nums[i] * temp_max, nums[i] * temp_min});
+      result = max(result, max_product);
+    }
+
+    return result;
+  }
 };