Fix knuthMorrisPratt for empty word request (trekhleb#101)

Author: dubzzz

src/algorithms/string/knuth-morris-pratt/__test__/knuthMorrisPratt.test.js

@@ -2,8 +2,8 @@ import knuthMorrisPratt from '../knuthMorrisPratt';
 
 describe('knuthMorrisPratt', () => {
   it('should find word position in given text', () => {
-    expect(knuthMorrisPratt('', '')).toBe(-1);
-    expect(knuthMorrisPratt('a', '')).toBe(-1);
+    expect(knuthMorrisPratt('', '')).toBe(0);
+    expect(knuthMorrisPratt('a', '')).toBe(0);
     expect(knuthMorrisPratt('a', 'a')).toBe(0);
     expect(knuthMorrisPratt('abcbcglx', 'abca')).toBe(-1);
     expect(knuthMorrisPratt('abcbcglx', 'bcgl')).toBe(3);

src/algorithms/string/knuth-morris-pratt/knuthMorrisPratt.js

@@ -30,6 +30,10 @@ function buildPatternTable(word) {
  * @return {number}
  */
 export default function knuthMorrisPratt(text, word) {
+  if (word.length === 0) {
+    return 0;
+  }
+
   let textIndex = 0;
   let wordIndex = 0;