Create alternating-digit-sum.cpp

Author: kamyu104

C++/alternating-digit-sum.cpp

@@ -0,0 +1,15 @@
+// Time:  O(logn)
+// Space: O(1)
+
+// math
+class Solution {
+public:
+    int alternateDigitSum(int n) {
+        int result = 0, sign = 1;
+        for (; n; n /= 10) {
+            sign *= -1;
+            result += sign * (n % 10);
+        }
+        return sign * result;
+    }
+};