Create number-of-ways-to-wear-different-hats-to-each-other.cpp

Author: kamyu104

C++/number-of-ways-to-wear-different-hats-to-each-other.cpp

@@ -0,0 +1,31 @@
+// Time:  O(h * 2^n)
+// Space: O(2^n)
+
+class Solution {
+public:
+    int numberWays(vector<vector<int>>& hats) {
+        static const int MOD = 1e9 + 7;
+        static const int HAT_SIZE = 40;
+
+        vector<vector<int>> hat_to_people(HAT_SIZE);
+        for (int i = 0; i < hats.size(); ++i) {
+            for (const auto& hat: hats[i]) {
+                hat_to_people[hat - 1].emplace_back(i);
+            }
+        }
+        vector<int> dp(1 << hats.size());
+        dp[0] = 1;    
+        for (const auto& people : hat_to_people) {
+            for (int mask = dp.size() - 1; mask >= 0; --mask) {
+                for (const int& p: people) {
+                    if (mask & (1 << p)) {
+                        continue;
+                    }
+                    dp[mask | (1 << p)] += dp[mask];
+                    dp[mask | (1 << p)] %= MOD;
+                }
+            }
+        }
+        return dp.back();
+    }
+};