@@ -0,0 +1,21 @@
+/**
+* @param {string} s
+* @return {number}
+*/
+var numberOfSubstrings = function (s) {
+let count = { 'a': 0, 'b': 0, 'c': 0 }; // Track character count
+let left = 0, result = 0;
+
+for (let right = 0; right < s.length; right++) {
+count[s[right]]++; // Expand window
+
+// When all characters are in the window, move left pointer
+while (count['a'] > 0 && count['b'] > 0 && count['c'] > 0) {
+result += s.length - right; // All substrings from left to end are valid
+count[s[left]]--;
+left++; // Shrink window
+}
+}
+
+return result;
+};