PHP finds the key in a two-dimensional array in one loop

PHP, as a powerful programming language, has rich data structures, among which two-dimensional array is a commonly used data structure. In daily development, we often need to traverse a two-dimensional array to find its key data. However, if nested loops are used for each traversal, the time complexity will become very high. This article will introduce a method to find the key value of a two-dimensional array in one loop.

1. What is a two-dimensional array?

A two-dimensional array is a special type of array that contains multiple arrays and organizes elements in rows and columns. A two-dimensional array can be thought of as a matrix consisting of multiple one-dimensional arrays, where each element can be accessed by a row index and a column index. In PHP, a two-dimensional array can be defined in the following way:

$arr = array(
    array(1, 2, 3),
    array(4, 5, 6),
    array(7, 8, 9)
);

The above code defines a $arr two-dimensional array, which contains three one-dimensional arrays, each one-dimensional array has three elements. .

2. Traditional two-dimensional array traversal method

In the traditional two-dimensional array traversal method, it is usually necessary to use two nested loops, one for traversing rows , and the other one is used to iterate over the columns. For example:

foreach ($arr as $key1 => $value1) {
    foreach ($value1 as $key2 => $value2) {
        if ($value2 == $target) {
            echo "关键值所在的行为：" . $key1 . "<br>";
            echo "关键值所在的列为：" . $key2 . "<br>";
        }
    }
}

In the above code, we use a foreach loop to iterate through each element in the $arr array. The first loop iterates through the rows and the second loop iterates over the columns. When the target element $target is found, output the row and column where the element is located.

However, the time complexity of this method is $O(n^2)$, that is, as the array size increases, the number of loops increases exponentially.

3. Method of finding the key value in one loop

Now, we introduce a more efficient method that can find the key value in a two-dimensional array in just one loop . This method is based on some array functions provided by PHP and has the advantage of a time complexity of $O(n)$.

First, we need to use PHP's array_map function to convert the two-dimensional array into a one-dimensional array, and then use the array_search function to find the target value in the one-dimensional array. The code is as follows:

// 将二维数组转成一维数组
$array = array_reduce($arr, 'array_merge', array());

// 在一维数组中查找目标值
$key = array_search($target, $array);

// 计算目标值所在的行和列
$row = floor($key / count($arr[0]));
$col = $key % count($arr[0]);

echo "关键值所在的行为：" . $row . "<br>";
echo "关键值所在的列为：" . $col . "<br>";

In the above code, we use the array_reduce function to convert the two-dimensional array into a one-dimensional array. The array_search function finds the target value in the one-dimensional array and calculates the target value in the two-dimensional array. rows and columns in .

The time complexity of this method is $O(n)$. Compared with the traditional method, the performance has been greatly improved.

4. Summary

This article introduces an efficient method that can find the key value of a two-dimensional array in one loop. By using some array functions provided by PHP, we reduced the time complexity from $O(n^2)$ to $O(n)$, greatly improving the performance of the program. I hope this article is helpful for traversing and searching two-dimensional arrays in PHP.

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