refactor(markdown): improve getMinNotPresentContinuousCount (#18138)

src/language-markdown/printer-markdown.js

@@ -182,7 +182,7 @@ function genericPrint(path, options, print) {
           ? node.value
           : node.value.replaceAll("\n", " ");
       const backtickCount = getMinNotPresentContinuousCount(code, "`");
-      const backtickString = "`".repeat(backtickCount || 1);
+      const backtickString = "`".repeat(backtickCount);
       const padding =
         code.startsWith("`") ||
         code.endsWith("`") ||

src/utils/get-min-not-present-continuous-count.js

@@ -1,9 +1,13 @@
 import escapeStringRegexp from "escape-string-regexp";
 
 /**
+ * Calculates the minimum `n` (>= 1) where `searchString.repeat(n)` is not present in `text`.
  * @param {string} text
  * @param {string} searchString
- * @returns {number}
+ * @example getMinNotPresentContinuousCount("```", "`") // 1
+ * @example getMinNotPresentContinuousCount("``` `", "`") // 2 (1 is occupied)
+ * @example getMinNotPresentContinuousCount("``` ` ``", "`") // 4 (1-3 are occupied)
+ * @returns {number} 1 if not exists, see the above example otherwise
  */
 function getMinNotPresentContinuousCount(text, searchString) {
   const matches = text.match(
@@ -11,7 +15,7 @@ function getMinNotPresentContinuousCount(text, searchString) {
   );
 
   if (matches === null) {
-    return 0;
+    return 1;
   }
 
   const countPresent = new Map();