Create number-of-substrings-with-only-1s.cpp

Author: kamyu104

C++/number-of-substrings-with-only-1s.cpp

@@ -0,0 +1,15 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    int numSub(string s) {
+        static const int MOD = 1e9 + 7;
+        int result = 0, count = 0;
+        for (const auto& c : s) {
+            count = (c == '1') ? count + 1 : 0;
+            result = (result + count) % MOD;
+        }
+        return result;
+    }
+};