How to find all array subsets in php

php method to find all array subsets: 1. Use the recursive method by splitting a large problem into multiple small problems, and then apply the same processing method to each small problem, and finally all The solutions to small problems are combined; 2. Use bitwise operations, first initialize the result to an empty array, and then use a loop to traverse all numbers from 0 to 2 to the nth power -1, with each number representing a subset. In the inner loop, bit operations are used to determine whether the current position is selected. If selected, the element with the corresponding bit is added to the subset. Finally, add the subset to the result array.

The operating environment of this tutorial: windows10 system, php8.1.3 version, DELL G3 computer.

In PHP development, array is a very commonly used data structure, which can be used to store a set of related data. Sometimes, we need to find all subsets of an array, that is, select a new array composed of any number of elements from the original array. This article will introduce how to use PHP to find all subsets of an array.

First of all, we need to clarify a concept: a subset of an array refers to a new array composed of 0 or more elements randomly selected from the original array. For example, the subsets of the original array [1, 2, 3] are: [], [1], [2], [3], [1, 2], [1, 3], [2, 3], [1, 2, 3].

Below we will introduce two commonly used methods to find all subsets of an array.

1. Use the recursive method

Recursion is an effective method to solve problems. It divides a large problem into multiple small problems, and then solves the problem in each Apply the same treatment method to each small problem, and finally combine the solutions of all small problems. In this method, we can use recursion to find all subsets of an array.

The specific implementation is as follows:

function subsets($nums) {
$result = [[]]; // 初始化结果，包含一个空集合
foreach ($nums as $num) {
$count = count($result); // 当前结果的数量
for ($i = 0; $i < $count; $i++) {
$newSubset = $result[$i]; // 获取当前结果集合
$newSubset[] = $num; // 加入当前元素
$result[] = $newSubset; // 加入结果数组
}
}
return $result;
}

In the above code, the first initialization result is an array containing an empty collection. Then iterate through each element in the original array, and for each element, add it to each subset in the result array, and add the new subset to the result array. Finally, the result array is returned.

2. Use bitwise operations

Another commonly used method to solve a subset of an array is to use bitwise operations. Because a subset of an array can be represented by a binary number, each bit of which indicates whether the element at that position is selected. For example, [1, 2, 3] There are 3 elements in total. A 3-digit binary number can be used to represent the subset. For example, 1 represents selected and 0 represents unselected. Therefore, the subset [1, 3] of [1, 2, 3] can be represented by the binary number 101. To represent.

The specific implementation is as follows:

function subsets($nums) {
$result = []; // 初始化结果为空数组
$n = count($nums); // 数组的长度
for ($i = 0; $i < pow(2, $n); $i++) {
$subset = []; // 初始化子集
for ($j = 0; $j < $n; $j++) {
if ($i & (1 << $j)) { // 使用位运算判断该位是否选中
$subset[] = $nums[$j]; // 若选中，则将该元素加入子集
}
}
$result[] = $subset; // 将子集加入结果数组
}
return $result;
}

In the above code, the first initialization result is an empty array. Then use a loop to iterate through all the numbers from 0 to 2-1, with each number representing a subset. In the inner loop, bit operations are used to determine whether the current position is selected. If selected, the elements at the corresponding position are added to the subset. Finally add the subset to the result array. Finally, the result array is returned.

Summary:

This article introduces two commonly used methods to find all subsets of an array, namely the recursive method and the bitwise operation method. These two methods can both achieve functions and have certain efficiency. In actual development, just choose the appropriate method according to specific needs. Through these methods, we can easily solve all subsets of an array, thus improving development efficiency

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