finished day 04 part 2

2024/04/example.txt

@@ -1,10 +1,10 @@
-MMMSXXMASM
+.M.S......
-MSAMXMSMSA
+..A..MSMS.
-AMXSXMAAMM
+.M.S.MAA..
-MSAMASMSMX
+..A.ASMSM.
-XMASAMXAMM
+.M.S.M....
-XXAMMXXAMA
+..........
-SMSMSASXSS
+S.S.S.S.S.
-SAXAMASAAA
+.A.A.A.A..
-MAMMMXMMMM
+M.M.M.M.M.
-MXMXAXMASX
+..........

2024/04/index.js

@@ -10,10 +10,9 @@ for (let y = 0; y < data.length; y++) {
     }
 }
 
-
 class Puzzle {
-
     #directions = []
+    #diagonals = []
     constructor() {
         this.i = 0
         this.solutions = 0
@@ -22,6 +21,9 @@ class Puzzle {
             [0, -1], [0, +1],
             [+1, -1], [+1, 0,], [+1, +1]
         ]
+        this.#diagonals = [
+            [-1, -1], [-1, +1]
+        ]
     }
     shootInDirection(y, x, dy, dx, length) {
         const positions = []
@@ -39,19 +41,6 @@ class Puzzle {
         return [...paper.filter(character => character.char === c)]
     }
 
-    getDirections(x, y) {
-        return [...new Set([
-            [Math.max(0, x - 1), Math.max(0, y - 1)],
-            [x, Math.max(0, y - 1)],
-            [Math.min(x + 1), Math.max(0, y - 1)],
-            [Math.max(0, x - 1), y],
-            [Math.min(x + 1), y],
-            [Math.max(x - 1), y + 1],
-            [x, Math.min(y + 1)],
-            [Math.min(x + 1), Math.min(y + 1)],
-        ])]
-    }
-
     isInBoundary(x, y) {
         let max_width = data[0].length
         let max_height = data.length
@@ -68,10 +57,21 @@ class Puzzle {
         }
         return true
     }
+    checkForWord2(d1, d2, word) {
+        const [y1, x1] = d1
+        const [y2, x2] = d2
 
+        if (!this.isInBoundary(x1, y1)) return false
+        if (!this.isInBoundary(x2, y2)) return false
+        const tl = this.isCharacterAt([...word][1], x1, y1) && this.isCharacterAt([...word][2], x2, y2) ? true : false
+        const tr = this.isCharacterAt([...word][2], x1, y1) && this.isCharacterAt([...word][1], x2, y2) ? true : false
+        return tl || tr
+    }
+    opposite(a) {
+        return -a
+    }
     solve(puzzle) {
-        console.log("--- solve ".padEnd(50, "-"))
+        console.log("--- solve part 1 ".padEnd(50, "-"))
-        const needed_length = puzzle.split('').length
         const word = puzzle.split('')
         const letter_positions = word.map(letter => { return { letter: letter, pos: this.findCharacter(letter).map(l => l.pos) } })
         const starting_letter = letter_positions[0]
@@ -86,7 +86,28 @@ class Puzzle {
         let total_words_possible = starting_letter.pos.length
         console.log(sum, "of possible", total_words_possible)
     }
+
+    solve2(puzzle) {
+        console.log("--- solve part 2 ".padEnd(50, "-"))
+        const word = puzzle.split('')
+        const letter_positions = word.map(letter => { return { letter: letter, pos: this.findCharacter(letter).map(l => l.pos) } })
+        const starting_letter = letter_positions[0]
+        let sum = 0
+        for (let i = 0; i < starting_letter.pos.length; i++) {
+            let letters_in_both_dirs = true
+            for (let j = 0; j < this.#diagonals.length; j++) {
+                let [dy, dx] = this.#diagonals[j]
+                let upper = this.shootInDirection(starting_letter.pos[i].y, starting_letter.pos[i].x, dy, dx, (word.length - 1) / 2)
+                let lower = this.shootInDirection(starting_letter.pos[i].y, starting_letter.pos[i].x, this.opposite(dy), this.opposite(dx), (word.length - 1) / 2)
+                if (!this.checkForWord2(upper.flat(), lower.flat(), word)) letters_in_both_dirs = false
+            }
+            sum += letters_in_both_dirs ? 1 : 0
+        }
+        let total_words_possible = starting_letter.pos.length
+        console.log(sum, "of possible", total_words_possible)
+    }
 }
 
 const p = new Puzzle()
-p.solve("XMAS")
+p.solve("XMAS")
+p.solve2("AMS")