Create day-of-the-year.cpp

Author: kamyu104

C++/day-of-the-year.cpp

@@ -0,0 +1,36 @@
+// Time:  O(1)
+// Space: O(1)
+
+class Solution {
+public:
+    Solution() : lookup_(12) {
+        for (int M = 1; M < lookup_.size(); ++M) {
+            lookup_[M] = lookup_[M - 1] + dayOfMonth(M);
+        }
+    }
+
+    int dayOfYear(string date) {   
+        const auto& result = split(date, '-');
+        const auto& Y = stoi(result[0]), &M = stoi(result[1]), &D = stoi(result[2]);
+        const auto& leap = (M > 2 && (((Y % 4 == 0) && (Y % 100 != 0)) || (Y % 400 == 0))) ? 1 : 0;
+        return lookup_[M - 1] + D + leap;
+    }
+
+private:
+    int dayOfMonth(int M) {
+        return (M == 2) ? 28 : 31 - (M - 1) % 7 % 2;
+    }
+    
+    vector<string> split(const string& s, const char delim) {
+        vector<string> result;
+        auto end = string::npos;
+        do {
+            const auto& start = end + 1;
+            end = s.find(delim, start);
+            result.emplace_back(s.substr(start, end - start));
+        } while (end != string::npos); 
+        return result;
+    }
+
+    vector<int> lookup_;
+};