Create number-of-days-in-a-month.cpp

Author: kamyu104

C++/number-of-days-in-a-month.cpp

@@ -0,0 +1,10 @@
+// Time:  O(1)
+// Space: O(1)
+
+class Solution {
+public:
+    int numberOfDays(int Y, int M) {
+        const auto& leap = (((Y % 4 == 0) && (Y % 100 != 0)) || (Y % 400 == 0)) ? 1 : 0;
+        return (M == 2) ? 28 + leap : 31 - (M - 1) % 7 % 2;
+    }
+};