Add solution #3084

Author: JoshCrozier

README.md

@@ -2162,6 +2162,7 @@
 3076|[Shortest Uncommon Substring in an Array](./solutions/3076-shortest-uncommon-substring-in-an-array.js)|Medium|
 3079|[Find the Sum of Encrypted Integers](./solutions/3079-find-the-sum-of-encrypted-integers.js)|Easy|
 3083|[Existence of a Substring in a String and Its Reverse](./solutions/3083-existence-of-a-substring-in-a-string-and-its-reverse.js)|Easy|
+3084|[Count Substrings Starting and Ending with Given Character](./solutions/3084-count-substrings-starting-and-ending-with-given-character.js)|Medium|
 3105|[Longest Strictly Increasing or Strictly Decreasing Subarray](./solutions/3105-longest-strictly-increasing-or-strictly-decreasing-subarray.js)|Easy|
 3108|[Minimum Cost Walk in Weighted Graph](./solutions/3108-minimum-cost-walk-in-weighted-graph.js)|Hard|
 3110|[Score of a String](./solutions/3110-score-of-a-string.js)|Easy|

solutions/3084-count-substrings-starting-and-ending-with-given-character.js

@@ -0,0 +1,21 @@
+/**
+ * 3084. Count Substrings Starting and Ending with Given Character
+ * https://leetcode.com/problems/count-substrings-starting-and-ending-with-given-character/
+ * Difficulty: Medium
+ *
+ * You are given a string s and a character c. Return the total number of substrings of s
+ * that start and end with c.
+ */
+
+/**
+ * @param {string} s
+ * @param {character} c
+ * @return {number}
+ */
+var countSubstrings = function(s, c) {
+  let count = 0;
+  for (const char of s) {
+    if (char === c) count++;
+  }
+  return (count * (count + 1)) / 2;
+};