Update 803-bricks-falling-when-hit.js

Author: everthis

803-bricks-falling-when-hit.js

@@ -66,3 +66,94 @@ const getConnectedCount = (grid, i, j) => {
     getConnectedCount(grid, i, j - 1)
   return count
 }
+
+// another
+
+/**
+ * @param {number[][]} grid
+ * @param {number[][]} hits
+ * @return {number[]}
+ */
+const hitBricks = function (grid, hits) {
+  const SPACE = 0
+  const BRICK = 1
+  const WILL_HIT = 2
+  const DIRECTIONS = [
+    [0, 1],
+    [1, 0],
+    [0, -1],
+    [-1, 0],
+  ]
+  const rows = grid.length
+  const cols = grid[0].length
+  const ds = new DisjointSet(rows * cols + 1)
+
+  for (const [hitR, hitC] of hits) {
+    if (grid[hitR][hitC] === BRICK) {
+      grid[hitR][hitC] = WILL_HIT
+    }
+  }
+
+  function hash(r, c) {
+    return r * cols + c + 1
+  }
+
+  function unionAround(r, c) {
+    const hashed = hash(r, c)
+    for (const [rDiff, cDiff] of DIRECTIONS) {
+      const rNext = r + rDiff
+      const cNext = c + cDiff
+      if (grid[rNext] !== undefined && grid[rNext][cNext] === BRICK) {
+        ds.union(hashed, hash(rNext, cNext))
+      }
+    }
+    if (r === 0) ds.union(0, hashed)
+  }
+  for (let i = 0; i < grid.length; i++) {
+    for (let j = 0; j < grid[i].length; j++) {
+      if (grid[i][j] === BRICK) unionAround(i, j)
+    }
+  }
+  let numBricksLeft = ds.size[ds.find(0)]
+  const numBricksDropped = new Array(hits.length)
+  // backwards
+  for (let i = hits.length - 1; i >= 0; i--) {
+    const [hitR, hitC] = hits[i]
+    if (grid[hitR][hitC] === WILL_HIT) {
+      grid[hitR][hitC] = BRICK
+      unionAround(hitR, hitC)
+      const newNumBricksLeft = ds.size[ds.find(0)]
+      numBricksDropped[i] = Math.max(newNumBricksLeft - numBricksLeft - 1, 0)
+      numBricksLeft = newNumBricksLeft
+    } else {
+      numBricksDropped[i] = 0
+    }
+  }
+  return numBricksDropped
+}
+
+class DisjointSet {
+  constructor(n) {
+    this.size = new Array(n).fill(1)
+    this.parent = new Array(n)
+    for (let i = 0; i < n; i++) {
+      this.parent[i] = i
+    }
+  }
+  find(x) {
+    if (x === this.parent[x]) return x
+    this.parent[x] = this.find(this.parent[x])
+
+    return this.parent[x]
+  }
+  union(x, y) {
+    const rootX = this.find(x)
+    const rootY = this.find(y)
+    if (rootX !== rootY) {
+      // attach X onto Y
+      this.parent[rootX] = rootY
+      this.size[rootY] += this.size[rootX]
+    }
+  }
+}
+