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2629. Function Composition.md

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2629. Function Composition.md

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2629. Function Composition Solved Easy

Given an array of functions [f1, f2, f3, ..., fn], return a new function fn that is the function composition of the array of functions. The function composition of [f(x), g(x), h(x)] is fn(x) = f(g(h(x))). The function composition of an empty list of functions is the identity function f(x) = x. You may assume each function in the array accepts one integer as input and returns one integer as output.

Example 1

Input: functions = [x => x + 1, x => x * x, x => 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

Example 2

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

Example 3

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

Constraints

  • -1000 <= x <= 1000
  • 0 <= functions.length <= 1000
  • all functions accept and return a single integer

📝 Solution 1 – reduceRight (সবচেয়ে সংক্ষিপ্ত)

/**
 * @param {Function[]} functions
 * @return {Function}
 */
var compose = function(functions) {
  return function(x) {
    return functions.reduceRight((acc, fn) => fn(acc), x);
  };
};

📝 Solution 2 – for লুপ (reverse করে)

/**
 * @param {Function[]} functions
 * @return {Function}
 */
var compose = function(functions) {
  return function(x) {
    let result = x;
    for (let i = functions.length - 1; i >= 0; i--) {
      result = functions[i](result);
    }
    return result;
  };
};

📝 Solution 3 – for...of + slice().reverse()

/**
 * @param {Function[]} functions
 * @return {Function}
 */
var compose = function(functions) {
  return function(x) {
    let result = x;
    for (const fn of functions.slice().reverse()) {
      result = fn(result);
    }
    return result;
  };
};

📝 Solution 4 – রিকার্সিভ (recursive)

/**
 * @param {Function[]} functions
 * @return {Function}
 */
var compose = function(functions) {
  if (functions.length === 0) return x => x; // identity
  
  return function(x) {
    // প্রথম ফাংশন বাদ দিয়ে বাকি ফাংশনের কম্পোজিশন বানাচ্ছি
    const [first, ...rest] = functions;
    const composedRest = compose(rest);
    return first(composedRest(x));
  };
};

✅ উদাহরণ

const functions = [x => x + 1, x => x * x, x => 2 * x];
const fn = compose(functions);

console.log(fn(4)); // Output: 65

🚀 কিভাবে কাজ করে:

  • আমরা একটি নতুন ফাংশন রিটার্ন করি যা ইনপুট x নেয়।

  • reduceRight ব্যবহার করে প্রতিটি ফাংশনকে ডান দিক থেকে বাঁ দিকে প্রয়োগ করি।

  • প্রতিটি ফাংশনের আউটপুট পরের ফাংশনের ইনপুট হয়।