Add C++ solution for leetcode 152.

Author: yanglr

cpp-leetcode/leetcode152-maximum-product-subarray_dp_no_array.cpp

@@ -0,0 +1,35 @@
+#include<vector>
+#include<algorithm>
+#include<iostream>
+using namespace std;
+
+class Solution {
+public:
+    int maxProduct(vector<int>& nums) {
+        int res = nums[0];  /* 1 <= nums.length <= 2 * 10^4, -10 <= nums[i] <= 10 */
+        int f = nums[0];    // f: 记录最大值f[i], g: 记录最小值g[i]
+        int g = nums[0];
+        const int N = nums.size();
+        for (int i = 1; i < N; i++)
+        {
+            int a_i = nums[i];
+            int fa = f*a_i;
+            int ga = g*a_i;
+            f = max(a_i, max(fa, ga));
+            g = min(a_i, min(fa, ga));
+            res = max(res, f);        // 更新最终的最大值
+        }
+        return res;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    vector<int> nums = {2, 3, -2, 4};
+    auto res = sol.maxProduct(nums);
+    cout << res << endl;
+
+    return 0;
+}