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CCT: Minor simplification of 'Shortest Path' solver (#1288)

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BFS shouldn't need some checks.
Also allows deletion of a helper file used by this function only.
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gmcew 2024-05-23 08:44:41 +01:00 committed by GitHub
parent 08eb60d21b
commit fe14d4fef3
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2 changed files with 7 additions and 147 deletions
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21
src/data/codingcontracttypes.ts
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@ -1,5 +1,4 @@
import { getRandomIntInclusive } from "../utils/helpers/getRandomIntInclusive";
import { MinHeap } from "../utils/Heap";
import { comprGenChar, comprLZGenerate, comprLZEncode, comprLZDecode } from "../utils/CompressionContracts";
import { HammingEncode, HammingDecode, HammingEncodeProperly } from "../utils/HammingCodeTools";
@ -994,7 +993,7 @@ export const codingContractTypesMetadata: ICodingContractTypeMetadata[] = [
const distance: [number][] = new Array(height);
//const prev: [[number, number] | undefined][] = new Array(height);
const queue = new MinHeap<[number, number]>();
const queue: [number, number][] = [];
for (let y = 0; y < height; y++) {
distance[y] = new Array(width).fill(Infinity) as [number];
@ -1015,21 +1014,15 @@ export const codingContractTypesMetadata: ICodingContractTypeMetadata[] = [
// Prepare starting point
distance[0][0] = 0;
queue.push([0, 0], 0);
queue.push([0, 0]);
// Take next-nearest position and expand potential paths from there
while (queue.size > 0) {
const [y, x] = queue.pop() as [number, number];
while (queue.length > 0) {
const [y, x] = queue.shift() as [number, number];
for (const [yN, xN] of neighbors(y, x)) {
const d = distance[y][x] + 1;
if (d < distance[yN][xN]) {
if (distance[yN][xN] == Infinity)
// Not reached previously
queue.push([yN, xN], d);
// Found a shorter path
else queue.changeWeight(([yQ, xQ]) => yQ == yN && xQ == xN, d);
//prev[yN][xN] = [y, x];
distance[yN][xN] = d;
if (distance[yN][xN] == Infinity) {
queue.push([yN, xN]);
distance[yN][xN] = distance[y][x] + 1;
}
}
}

133
src/utils/Heap.ts
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@ -1,133 +0,0 @@
/** Binary heap. */
abstract class BinHeap<T> {
/**
* Heap data array consisting of [weight, payload] pairs, arranged by weight
* to satisfy heap condition.
*
* Encodes the binary tree by storing tree root at index 0 and
* left child of element i at `i * 2 + 1` and
* right child of element i at `i * 2 + 2`.
*/
protected data: [number, T][];
constructor() {
this.data = [];
}
/** Get number of elements in the heap. */
public get size(): number {
return this.data.length;
}
/** Add a new element to the heap. */
public push(value: T, weight: number): void {
const i = this.data.length;
this.data[i] = [weight, value];
this.heapifyUp(i);
}
/** Get the value of the root-most element of the heap, without changing the heap. */
public peek(): T | undefined {
if (this.data.length == 0) return undefined;
return this.data[0][1];
}
/** Remove the root-most element of the heap and return the removed element's value. */
public pop(): T | undefined {
if (this.data.length == 0) return undefined;
const value = this.data[0][1];
this.data[0] = this.data[this.data.length - 1];
this.data.length = this.data.length - 1;
this.heapifyDown(0);
return value;
}
/** Change the weight of an element in the heap. */
public changeWeight(predicate: (value: T) => boolean, weight: number): void {
// Find first element with matching value, if any
const i = this.data.findIndex((e) => predicate(e[1]));
if (i == -1) return;
// Update that element's weight
this.data[i][0] = weight;
// And re-heapify if needed
const p = Math.floor((i - 1) / 2);
if (!this.heapOrderABeforeB(this.data[p][0], this.data[i][0]))
// Needs to shift root-wards?
this.heapifyUp(i);
// Try shifting deeper
else this.heapifyDown(i);
}
/** Restore heap condition, starting at index i and traveling towards root. */
protected heapifyUp(i: number): void {
// Swap the new element up towards root until it reaches root position or
// settles under under a suitable parent
while (i > 0) {
const p = Math.floor((i - 1) / 2);
// Reached heap-ordered state already?
if (this.heapOrderABeforeB(this.data[p][0], this.data[i][0])) break;
// Swap
const tmp = this.data[p];
this.data[p] = this.data[i];
this.data[i] = tmp;
// And repeat at parent index
i = p;
}
}
/** Restore heap condition, starting at index i and traveling away from root. */
protected heapifyDown(i: number): void {
// Swap the shifted element down in the heap until it either reaches the
// bottom layer or is in correct order relative to it's children
while (i < this.data.length) {
const l = i * 2 + 1;
const r = i * 2 + 2;
let toSwap = i;
// Find which one of element i and it's children should be closest to root
if (l < this.data.length && this.heapOrderABeforeB(this.data[l][0], this.data[toSwap][0])) toSwap = l;
if (r < this.data.length && this.heapOrderABeforeB(this.data[r][0], this.data[toSwap][0])) toSwap = r;
// Already in order?
if (i == toSwap) break;
// Not in order. Swap child that should be closest to root up to 'i' and repeat
const tmp = this.data[toSwap];
this.data[toSwap] = this.data[i];
this.data[i] = tmp;
i = toSwap;
}
}
/**
* Should element with weight `weightA` be closer to root than element with
* weight `weightB`?
*/
protected abstract heapOrderABeforeB(weightA: number, weightB: number): boolean;
}
/** Binary max-heap. */
export class MaxHeap<T> extends BinHeap<T> {
heapOrderABeforeB(weightA: number, weightB: number): boolean {
return weightA > weightB;
}
}
/** Binary min-heap. */
export class MinHeap<T> extends BinHeap<T> {
heapOrderABeforeB(weightA: number, weightB: number): boolean {
return weightA < weightB;
}
}