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Author: assassint2017

Bitwise ORs of Subarrays/Bitwise_ORs_of_Subarrays.cpp

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+// 这道题目最直接的方法明显是n3的时间复杂度
+// 稍微优化一点就是n2的时间复杂度，常数的空间复杂度
+// 加速的思路可以做到线性的时间复杂度，附参考链接如下
+// https://leetcode.com/problems/bitwise-ors-of-subarrays/discuss/165859/C%2B%2B-O(kN)-solution
+
+// Runtime: 1380 ms, faster than 41.00% of C++ online submissions for Bitwise ORs of Subarrays.
+// Memory Usage: 299.4 MB, less than 66.67% of C++ online submissions for Bitwise ORs of Subarrays.
+
+class Solution 
+{
+public:
+    int subarrayBitwiseORs(vector<int>& A) 
+    {
+        unordered_set<int> res, hs1;
+        for (int item : A)
+        {
+            unordered_set<int> hs2;
+            for (int iitem : hs1)
+                hs2.insert(item | iitem);
+            hs2.insert(item);
+            
+            hs1 = hs2;
+            
+            for (int iitem : hs2)
+                res.insert(iitem);
+        }
+        return res.size();
+    }
+};