function-composition

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JavaScript

Given an array of functions&nbsp;<code>[f1, f2, f3,&nbsp;..., fn]</code>, return&nbsp;a new function&nbsp;<code>fn</code>&nbsp;that is the function&nbsp;composition of the array of functions.

The&nbsp;function&nbsp;composition&nbsp;of&nbsp;<code>[f(x), g(x), h(x)]</code>&nbsp;is&nbsp;<code>fn(x) = f(g(h(x)))</code>.

The&nbsp;function&nbsp;composition&nbsp;of an empty list of functions is the&nbsp;identity function&nbsp;<code>f(x) = x</code>.

You may assume each&nbsp;function&nbsp;in the array accepts one integer as input&nbsp;and returns one integer as output.

&nbsp;
Example 1:

<pre>
Input: functions = [x =&gt; x + 1, x =&gt; x * x, x =&gt; 2 * x], x = 4
Output: 65
Explanation:
Evaluating from right to left ...
Starting with x = 4.
2 * (4) = 8
(8) * (8) = 64
(64) + 1 = 65
</pre>

Example 2:

<pre>
Input: functions = [x =&gt; 10 * x, x =&gt; 10 * x, x =&gt; 10 * x], x = 1
Output: 1000
Explanation:
Evaluating from right to left ...
10 * (1) = 10
10 * (10) = 100
10 * (100) = 1000
</pre>

Example 3:

<pre>
Input: functions = [], x = 42
Output: 42
Explanation:
The composition of zero functions is the identity function</pre>

&nbsp;
Constraints:

<ul>
	<li><code>-1000 &lt;= x &lt;= 1000</code></li>
	<li><code>0 &lt;= functions.length &lt;= 1000</code></li>
	<li>all functions accept and return a single integer</li>
</ul>

compose

Function Composition

Memoize

memoize

记忆函数

Counter

counter

计数器

请你编写一个函数，它接收一个函数数组 <code>[f1, f2, f3，…， fn]</code> ，并返回一个新的函数 <code>fn</code>&nbsp;，它是函数数组的 复合函数 。

<code>[f(x)， g(x)， h(x)]</code> 的 复合函数 为 <code>fn(x) = f(g(h(x)))</code>&nbsp;。

一个空函数列表的 复合函数 是 恒等函数 <code>f(x) = x</code> 。

你可以假设数组中的每个函数接受一个整型参数作为输入，并返回一个整型作为输出。

&nbsp;

示例 1：

<pre>
输入：functions = [x =&gt; x + 1, x =&gt; x * x, x =&gt; 2 * x], x = 4
输出：65
解释：
从右向左计算......
Starting with x = 4.
2 * (4) = 8
(8) * (8) = 64
(64) + 1 = 65
</pre>

示例 2：

<pre>
输入：functions = [x =&gt; 10 * x, x =&gt; 10 * x, x =&gt; 10 * x], x = 1
输出：1000
解释：
从右向左计算......
10 * (1) = 10
10 * (10) = 100
10 * (100) = 1000
</pre>

示例 3：

<pre>
输入：functions = [], x = 42
输出：42
解释：
空函数列表的复合函数就是恒等函数</pre>

&nbsp;

提示：

<ul>
	<li><code>-1000 &lt;= x &lt;= 1000</code></li>
	<li><code>0 &lt;= functions.length &lt;= 1000</code></li>
	<li>所有函数都接受并返回一个整型</li>
</ul>