Create sum-multiples.cpp

Author: kamyu104

C++/sum-multiples.cpp

@@ -0,0 +1,14 @@
+// Time:  O(1)
+// Space: O(1)
+
+// math, principle of inclusion and exclusion
+class Solution {
+public:
+    int sumOfMultiples(int n) {
+        const auto& f = [&](int d) {
+            return d * (1 + (n / d)) * (n / d) / 2;
+        };
+
+        return (f(3) + f(5) + f(7)) - (f(3 * 5) + f(5 * 7) + f(7 * 3)) + f(3 * 5 * 7);
+    }
+};