Create 2812-find-the-safest-path-in-a-grid.js

Author: everthis

2812-find-the-safest-path-in-a-grid.js

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+/**
+ * @param {number[][]} grid
+ * @return {number}
+ */
+const maximumSafenessFactor = function (grid) {
+  let n = grid.length,
+    m = grid[0].length,
+    ans = Infinity
+  const { min, abs } = Math
+  let t = []
+  for (let i = 0; i < n; i++) {
+    for (let j = 0; j < m; j++) {
+      if (grid[i][j] == 1) {
+        t.push([i, j]) // keeping track of each thief
+      }
+    }
+  }
+
+  const vis = Array.from({ length: n }, () => Array(m).fill(0))
+
+  const pq = new PQ((a, b) => a[0] > b[0])
+  let m_dist = Infinity
+  for (const thieve of t) {
+    m_dist = Math.min(m_dist, thieve[0] + thieve[1]) // Calculating Manhattan distance between current cell and all thieves
+  }
+  let dr = [0, -1, 0, 1],
+    dc = [-1, 0, 1, 0]
+  pq.push([m_dist, [0, 0]])
+  vis[0][0] = 1
+  // int mn_dist = 0;
+  while (!pq.isEmpty()) {
+    let temp = pq.pop()
+
+    let dist = temp[0],
+      r = temp[1][0],
+      c = temp[1][1]
+    // mn_dist = min(dist,mn_dist);
+    if (r == n - 1 && c == m - 1) {
+      return dist // return path safety when end is reached
+    }
+    for (let i = 0; i < 4; i++) {
+      let nr = r + dr[i]
+      let nc = c + dc[i]
+      if (nr >= 0 && nc >= 0 && nr < n && nc < m && !vis[nr][nc]) {
+        //for every adjacent cell calculate the minimum mahattan distance betwwen cell and thieves.
+        vis[nr][nc] = 1
+        let m_dist = Infinity
+        for (let thieve of t) {
+          m_dist = min(m_dist, abs(thieve[0] - nr) + abs(thieve[1] - nc))
+        }
+
+        // push the minimum of current distance and the minimum distance of the path till now
+        pq.push([min(m_dist, dist), [nr, nc]])
+      }
+    }
+  }
+  return ans
+}
+
+class PQ {
+  constructor(comparator = (a, b) => a > b) {
+    this.heap = []
+    this.top = 0
+    this.comparator = comparator
+  }
+  size() {
+    return this.heap.length
+  }
+  isEmpty() {
+    return this.size() === 0
+  }
+  peek() {
+    return this.heap[this.top]
+  }
+  push(...values) {
+    values.forEach((value) => {
+      this.heap.push(value)
+      this.siftUp()
+    })
+    return this.size()
+  }
+  pop() {
+    const poppedValue = this.peek()
+    const bottom = this.size() - 1
+    if (bottom > this.top) {
+      this.swap(this.top, bottom)
+    }
+    this.heap.pop()
+    this.siftDown()
+    return poppedValue
+  }
+  replace(value) {
+    const replacedValue = this.peek()
+    this.heap[this.top] = value
+    this.siftDown()
+    return replacedValue
+  }
+
+  parent = (i) => ((i + 1) >>> 1) - 1
+  left = (i) => (i << 1) + 1
+  right = (i) => (i + 1) << 1
+  greater = (i, j) => this.comparator(this.heap[i], this.heap[j])
+  swap = (i, j) => ([this.heap[i], this.heap[j]] = [this.heap[j], this.heap[i]])
+  siftUp = () => {
+    let node = this.size() - 1
+    while (node > this.top && this.greater(node, this.parent(node))) {
+      this.swap(node, this.parent(node))
+      node = this.parent(node)
+    }
+  }
+  siftDown = () => {
+    let node = this.top
+    while (
+      (this.left(node) < this.size() && this.greater(this.left(node), node)) ||
+      (this.right(node) < this.size() && this.greater(this.right(node), node))
+    ) {
+      let maxChild =
+        this.right(node) < this.size() &&
+        this.greater(this.right(node), this.left(node))
+          ? this.right(node)
+          : this.left(node)
+      this.swap(node, maxChild)
+      node = maxChild
+    }
+  }
+}