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GeezerVison is showing github.com — JavaScript/Graphs/LCABinaryLifting.js at master · hackingstaar/JavaScript Expand file tree/ Copy pathLCABinaryLifting.jsMore file actions 61 lines (54 loc) · 1.93 KB / Copy pathLCABinaryLifting.jsFile metadata and controls61 lines (54 loc) · 1.93 KB 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 /** * Author: Adrito Mukherjee * Finding Lowest Common Ancestor By Binary Lifting implementation in JavaScript * The technique requires preprocessing the tree in O(N log N) using dynamic programming) * It can be used to find Lowest Common Ancestor of two nodes in O(log N) * Tutorial on Lowest Common Ancestor: https://www.geeksforgeeks.org/lca-in-a-tree-using-binary-lifting-technique */ import { BinaryLifting } from './BinaryLifting' class LCABinaryLifting extends BinaryLifting { constructor(root, tree) { super(root, tree) this.depth = new Map() // depth[node] stores the depth of node from root this.depth.set(root, 1) this.dfsDepth(root, root) } dfsDepth(node, parent) { // DFS to find depth of every node in the tree for (const child of this.connections.get(node)) { if (child !== parent) { this.depth.set(child, this.depth.get(node) + 1) this.dfsDepth(child, node) } } } getLCA(node1, node2) { // We make sure that node1 is the deeper node among node1 and node2 if (this.depth.get(node1) < this.depth.get(node2)) { ;[node1, node2] = [node2, node1] } // We check if node1 is the ancestor of node2, and if so, then return node1 const k = this.depth.get(node1) - this.depth.get(node2) node1 = this.kthAncestor(node1, k) if (node1 === node2) { return node1 } for (let i = this.log - 1; i >= 0; i--) { if (this.up.get(node1).get(i) !== this.up.get(node2).get(i)) { node1 = this.up.get(node1).get(i) node2 = this.up.get(node2).get(i) } } return this.up.get(node1).get(0) } } function lcaBinaryLifting(root, tree, queries) { const graphObject = new LCABinaryLifting(root, tree) const lowestCommonAncestors = [] for (const [node1, node2] of queries) { const lca = graphObject.getLCA(node1, node2) lowestCommonAncestors.push(lca) } return lowestCommonAncestors } export default lcaBinaryLifting |
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