Javascript 记忆化实施

Question

我一直在和同事讨论这个话题。我想从你们那里知道，这是否真的是实现记忆的正确方法。

function memoize(result) {
  let cache = {};

  return function() {
    if (cache[result]) {
      // returns cached result / no calculation
      return cache[result];
    }
    // calculating...
    cache[result] = result;
    return cache[result];
  };
}

function expensiveCalculation() {
  let counter = 0;
  for (let i = 0; i < 1000000; i++) {
    counter += i;
  }
  return counter;
}

console.time("FirstCalculation");
const memoizedExpensiveCalculation = memoize(expensiveCalculation());
console.timeEnd("FirstCalculation");

console.time("1_Memoized");
memoizedExpensiveCalculation();
console.timeEnd("1_Memoized");

console.time("2_Memoized");
memoizedExpensiveCalculation();
console.timeEnd("2_Memoized");

console.time("3_Memoized");
memoizedExpensiveCalculation();
console.timeEnd("3_Memoized");

时间日志显示，事实上，第一次花费的时间要长得多（这是我们所期望的），之后花费的时间更少。

Answer 1

不正确

您显示的代码

function memoize(result) {
  let cache = {};

  return function() {
    if (cache[result]) {
      // returns cached result / no calculation
      return cache[result];
    }
    // calculating...
    cache[result] = result;
    return cache[result];
  };
}

基本上是

function memoize(result) {
  return result
}

在记忆中你缓存的是input/output对并在输入匹配时跳过真正的函数调用。

Answer 2

类似于：

function get(func) {
  let cache = {};

  return function(key) {
    if (key in cache) {
      return cache[key];
    }
    cache[key] = func(key);
    return cache[key];
 };
}

function expensiveCalculation(param) {
  console.log('expensive calculation runs')
  let counter = 0;
  for (let i = 0; i < 10000; i++) {
    counter += i;
  }
  return param*2;
}
const memo = get(expensiveCalculation)
console.log('start')
console.log('first try');
console.log(memo(10));
console.log('second try');
console.log(memo(10));

Javascript 记忆化实施

Javascript Memoization Implementation

javascript

memoization