Create count-pairs-that-form-a-complete-day-i.cpp

Author: kamyu104

C++/count-pairs-that-form-a-complete-day-i.cpp

@@ -0,0 +1,34 @@
+// Time:  O(n + 24)
+// Space: O(24)
+
+// freq table
+class Solution {
+public:
+    int countCompleteDayPairs(vector<int>& hours) {
+        int result = 0;
+        vector<int> cnt(24);
+        for (const auto& x : hours) {
+            result += cnt[((-x % 24) + 24) % 24];
+            ++cnt[x % 24];
+        }
+        return result;
+    }
+};
+
+// Time:  O(n^2)
+// Space: O(1)
+// brute force
+class Solution2 {
+public:
+    int countCompleteDayPairs(vector<int>& hours) {
+        int result = 0;
+        for (int i = 0; i + 1 < size(hours); ++i) {
+            for (int j = i + 1; j < size(hours); ++j) {
+                if ((hours[i] + hours[j]) % 24 == 0) {
+                    ++result;
+                }
+            }
+        }
+        return result;
+    }
+};