Create number-of-equal-count-substrings.cpp

Author: kamyu104

C++/number-of-equal-count-substrings.cpp

@@ -0,0 +1,22 @@
+// Time:  O(26 * n) = O(n)
+// Space: O(26) = O(1)
+
+class Solution {
+public:
+    int equalCountSubstrings(string s, int count) {
+        int result = 0;
+        const int max_l = min(size(unordered_set<char>(cbegin(s), cend(s))), size(s) / count);
+        for (int l = 1; l <= max_l; ++l) {
+            unordered_map<char, int> cnt;
+            for (int i = 0, equal_cnt = 0; i < size(s); ++i) {
+                equal_cnt += static_cast<int>(++cnt[s[i]] == count);
+                if (i >= count * l) {
+                    equal_cnt -= static_cast<int>(cnt[s[i - count * l]]-- == count);
+                }
+                result += static_cast<int>(equal_cnt == l);
+                
+            }
+        }
+        return result;
+    }
+};