Create substrings-of-size-three-with-distinct-characters.cpp

Author: kamyu104

C++/substrings-of-size-three-with-distinct-characters.cpp

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+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    int countGoodSubstrings(string s) {
+        static const int K = 3;
+
+        int result = 0;
+        unordered_map<int, int> count;
+        for (int i = 0; i < size(s); ++i) {
+            if (i >= K) {
+                if (--count[s[i - K]] == 0) {
+                    count.erase(s[i - K]);
+                }
+            }
+            ++count[s[i]];
+            if (size(count) == K) {
+                ++result;
+            }
+        }
+        return result;
+    }
+};