Create unique-substrings-with-equal-digit-frequency.cpp

Author: kamyu104

C++/unique-substrings-with-equal-digit-frequency.cpp

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+// Time:  O(n^2)
+// Space: O(n^2)
+
+// rolling hash
+class Solution {
+public:
+    int equalDigitFrequency(string s) {
+        static const int MOD = 1e9 + 7;
+        static const int D = 27;
+
+        unordered_set<int> lookup;
+        for (int i = 0; i < size(s); ++i) {
+            unordered_map<int, int> cnt;
+            int64_t h = 0;
+            int max_cnt = 0;
+            for (int j = i; j < size(s); ++j) {
+                const int d = s[j] - '0' + 1;
+                h = (h * D + d) % MOD;
+                ++cnt[d];
+                max_cnt = max(max_cnt, cnt[d]);
+                if (size(cnt) * max_cnt == j - i + 1) {
+                    lookup.emplace(h);
+                }
+            }
+        }
+        return size(lookup);
+    }
+};