Create 1976-number-of-ways-to-arrive-at-destination.js

Author: everthis

1976-number-of-ways-to-arrive-at-destination.js

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+/**
+ * @param {number} n
+ * @param {number[][]} roads
+ * @return {number}
+ */
+const countPaths = function(n, roads) {
+  const graph = {}
+  for(let r of roads) {
+    const [u, v, t] = r
+    if(graph[u] == null) graph[u] = []
+    if(graph[v] == null) graph[v] = []
+    graph[u].push([v, t])
+    graph[v].push([u, t])
+  }
+  
+  return dijkstra(graph, n, 0)
+
+  function dijkstra(graph, n, src) {
+    const dist = Array(n).fill(Infinity)
+    const ways = Array(n).fill(0), mod = 1e9 + 7
+    ways[src] = 1
+    dist[src] = 0
+    const pq = new PriorityQueue((a, b) => a[0] === b[0] ? a[1] < b[1] : a[0] < b[0])
+    pq.push([0, 0])
+    while(!pq.isEmpty()) {
+      const [d, u] = pq.pop()
+      if(d > dist[u]) continue
+      if(graph[u] == null) graph[u] = []
+      for(const [v, time] of graph[u]) {
+        if(dist[v] > d + time) {
+          ways[v] = ways[u]
+          dist[v] = d + time
+          pq.push([dist[v], v])
+        } else if(dist[v] === d + time) {
+          ways[v] = (ways[v] + ways[u]) % mod
+        }
+      }
+    }
+    return ways[n - 1]
+  }
+  
+};
+  
+class PriorityQueue {
+  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
+    }
+  }
+}
+