Pascal's Triangle

demo

Pascal's Triangle

c(m,n)

import { caching } from '../decorator/caching.js';

// binomial combinations
function _c(m, n) {
  if (m - n < 0 || n < 0) return 0;
  if (m - n === 0 || n === 0) return 1;
  return _c(m - 1, n - 1) + _c(m - 1, n);
}

// give 'memory' to function '_c'
export const c = caching(_c);

caching decorator

caching(f)

// ⭐️ caching decorator
//    use a closure to ecapsulate 'f'
export function caching(f) {
  // make a new cache for this 'f'
  let cache = new Map();

  // returns a function that can remember
  return function (...args) {
    // if not in cache, cache it.
    const key = `${args}`;
    if (!cache.has(key)) {
      //          ╭- call a method -╮  ('f' could be a method)
      let value = f.apply(this, args); // ⭐️ with "this" context
      cache.set(key, value);
      // log(`(${key}, ${value}) cached ...`);
    }
    // get function value from cache
    return cache.get(key);
  };
}

📗 參考

• JS.info ⟩ Decorators and forwarding, call/apply

• PJCHENder ⟩ [演算法] Fibonacci：善用 cache 和 Memoization 提升程式效能

💾 程式

• codesandbox - Pascal Triangle

• replit - decorating methods