Create count-substrings-that-satisfy-k-constraint-i.cpp

Author: kamyu104

C++/count-substrings-that-satisfy-k-constraint-i.cpp

@@ -0,0 +1,18 @@
+// Time:  O(n)
+// Space: O(1)
+
+// two pointers, sliding window
+class Solution {
+public:
+    int countKConstraintSubstrings(string s, int k) {
+        int result = 0;
+        for (int right = 0, left = 0, cnt = 0; right < size(s); ++right) {
+            cnt += s[right] == '1' ? 1 : 0;
+            while (!(cnt <= k || (right - left + 1) - cnt <= k)) {
+                cnt -= s[left++] == '1' ? 1 : 0;
+            }
+            result += right - left + 1;
+        }
+        return result;
+    }
+};