suggestionList: reuse matrix array

Author: IvanGoncharov

src/jsutils/suggestionList.js

@@ -9,9 +9,11 @@ export default function suggestionList(
   options: $ReadOnlyArray<string>,
 ): Array<string> {
   const optionsByDistance = Object.create(null);
+  const lexicalDistance = new LexicalDistance(input);
+
   const inputThreshold = input.length / 2;
   for (const option of options) {
-    const distance = lexicalDistance(input, option);
+    const distance = lexicalDistance.measure(option);
     const threshold = Math.max(inputThreshold, option.length / 2, 1);
     if (distance <= threshold) {
       optionsByDistance[option] = distance;
@@ -36,50 +38,60 @@ export default function suggestionList(
  * of 1.
  *
  * This distance can be useful for detecting typos in input or sorting
- *
- * @param {string} a
- * @param {string} b
- * @return {int} distance in number of edits
  */
-function lexicalDistance(aStr, bStr) {
-  if (aStr === bStr) {
-    return 0;
+class LexicalDistance {
+  _input: string;
+  _inputLowerCase: string;
+  _cells: Array<Array<number>>;
+
+  constructor(input: string) {
+    this._input = input;
+    this._inputLowerCase = input.toLowerCase();
+    this._cells = [];
   }
 
-  const d = [];
-  const a = aStr.toLowerCase();
-  const b = bStr.toLowerCase();
-  const aLength = a.length;
-  const bLength = b.length;
+  measure(option: string): number {
+    if (this._input === option) {
+      return 0;
+    }
 
-  // Any case change counts as a single edit
-  if (a === b) {
-    return 1;
-  }
+    const optionLowerCase = option.toLowerCase();
 
-  for (let i = 0; i <= aLength; i++) {
-    d[i] = [i];
-  }
+    // Any case change counts as a single edit
+    if (this._inputLowerCase === optionLowerCase) {
+      return 1;
+    }
 
-  for (let j = 1; j <= bLength; j++) {
-    d[0][j] = j;
-  }
+    const d = this._cells;
+    const a = optionLowerCase;
+    const b = this._inputLowerCase;
+    const aLength = a.length;
+    const bLength = b.length;
+
+    for (let i = 0; i <= aLength; i++) {
+      d[i] = [i];
+    }
 
-  for (let i = 1; i <= aLength; i++) {
     for (let j = 1; j <= bLength; j++) {
-      const cost = a[i - 1] === b[j - 1] ? 0 : 1;
+      d[0][j] = j;
+    }
 
-      d[i][j] = Math.min(
-        d[i - 1][j] + 1,
-        d[i][j - 1] + 1,
-        d[i - 1][j - 1] + cost,
-      );
+    for (let i = 1; i <= aLength; i++) {
+      for (let j = 1; j <= bLength; j++) {
+        const cost = a[i - 1] === b[j - 1] ? 0 : 1;
 
-      if (i > 1 && j > 1 && a[i - 1] === b[j - 2] && a[i - 2] === b[j - 1]) {
-        d[i][j] = Math.min(d[i][j], d[i - 2][j - 2] + cost);
+        d[i][j] = Math.min(
+          d[i - 1][j] + 1,
+          d[i][j - 1] + 1,
+          d[i - 1][j - 1] + cost,
+        );
+
+        if (i > 1 && j > 1 && a[i - 1] === b[j - 2] && a[i - 2] === b[j - 1]) {
+          d[i][j] = Math.min(d[i][j], d[i - 2][j - 2] + cost);
+        }
       }
     }
-  }
 
-  return d[aLength][bLength];
+    return d[aLength][bLength];
+  }
 }