fix(2018 day-14): catch patterns that occur at search buffer breaks

Author: developher-net

2018/day-14/recipes.js

@@ -135,22 +135,31 @@ const calculateXAfterY = (x, y, recipes) => {
  * Counts how many recipes are to the left of the specified pattern
  * @param {String} pattern to search for
  * @param {LinkedList} recipes recipe list
- * @param {Number} bufferSize bucket size to search. Tuning bucket size can improve speed but may risk missing match if the match crosses buckets.
+ * @param {Number} bufferSize bucket size to search. Tuning bucket size can improve speed by adjusting memory usage.
  */
 const findPattern = (pattern, recipes, bufferSize) => {
   bufferSize = bufferSize || 101
   let matched = false
   let position = recipes.length
+  let overlapBuffer = ''
+
   while (matched !== true) {
+    console.log(`Checking for ${pattern} in segement starting at ${position}`)
     let haystack = loopRecipesForElves(recipes, bufferSize)
+
     let offset = haystack.indexOf(pattern)
+
+    position = (offset >= 0) ? position + offset : recipes.length
     if (offset > -1) {
-      position += offset
-      console.log(`Found ${pattern} at ${haystack.substr(0, offset + pattern.length)}`)
+      // console.log(`Found ${pattern} at ${haystack.substr(0, offset + pattern.length)}`)
+      matched = true
+    }
+    // Use another small buffer to check the string that overlaps the split between buffer segements
+    overlapBuffer = overlapBuffer.substr(overlapBuffer.length - 1 - pattern.length, pattern.length)
+    overlapBuffer += haystack.substr(0, pattern.length)
+    if (overlapBuffer.indexOf(pattern) > -1) {
+      position = position - pattern.length + overlapBuffer.indexOf(pattern)
       matched = true
-    } else {
-      position += bufferSize
-      console.log(`Did not find ${pattern} before ${position}`)
     }
   }
 

2018/day-14/recipes.test.js

@@ -104,24 +104,26 @@ describe('--- Day 14: Chocolate Charts ---', () => {
         const actual = findPattern('51589', recipes)
         expect(actual).to.equal(9)
       })
-    })
-    describe('findPattern()', () => {
       it('counts the number of recipes to the left of the specified pattern', () => {
         const actual = findPattern('01245', recipes)
         expect(actual).to.equal(5)
       })
-    })
-    describe('findPattern()', () => {
       it('counts the number of recipes to the left of the specified pattern', () => {
         const actual = findPattern('92510', recipes)
         expect(actual).to.equal(18)
       })
-    })
-    describe('findPattern()', () => {
       it('counts the number of recipes to the left of the specified pattern', () => {
         const actual = findPattern('59414', recipes)
         expect(actual).to.equal(2018)
       })
+      it('accepts small search buffer sizes', () => {
+        const actual = findPattern('59414', recipes, 20)
+        expect(actual).to.equal(2018)
+      })
+      it('accepts large search buffer sizes', () => {
+        const actual = findPattern('59414', recipes, 50000)
+        expect(actual).to.equal(2018)
+      })
     })
   })
 })

2018/day-14/solution.js

@@ -1,6 +1,7 @@
 const {
   calculateXAfterY,
   findPattern,
+  loopRecipesForElves,
   Recipes
 } = require('./recipes')
 
@@ -13,16 +14,13 @@ const answer = calculateXAfterY(10, input, recipes)
 console.log(`-- Part 1 --`)
 console.log(`Answer: ${answer}`)
 
-elves = [3, 7]
-recipes = new Recipes(elves[0])
-elves.forEach((elf, idx) => {
-  if (idx === 0) {
-    elves[0] = recipes.head
-  } else {
-    elves[idx] = recipes.addRecipe(elf)
-  }
-})
-const bufferSize = 10001
-const answer2 = findPattern(input.toString(), recipes, elves, bufferSize)
+recipes = new Recipes([3, 7])
+while (recipes.length < 3000) {
+  loopRecipesForElves(recipes, 1)
+}
+
+recipes = new Recipes([3, 7])
+const bufferSize = 10000
+const answer2 = findPattern(input.toString(), recipes, bufferSize)
 console.log(`-- Part 2 --`)
 console.log(`Answer: ${answer2}`)