What are L, R, K, and N in an array?

In different contexts, "L" and "R" can represent different things, such as indices, values, or operations. Below are some common interpretations:

1. L and R as Indices in an Array:
If you are working with an array and you encounter "L" and "R", they might represent the left index (L) and the right index (R) of a subarray, often used in range-related problems. For example:
L = 0 (leftmost index)
R = n-1 (rightmost index, where n is the length of the array)
These indices are commonly used in problems like:
Subarray sum: Sum of elements between indices L and R.
Search: Binary search or range queries between indices L and R.
Divide and conquer algorithms that break an array into parts from L to R.

2. L and R as Partitioning Values:
In problems like QuickSort, "L" and "R" might refer to pivot values or ranges where the array is being split into two parts. This is common in partitioning logic:
L could be the "low" value.
R could be the "high" value.

3. L and R as Operations:
If you have an array, "L" and "R" could also represent certain operations to apply within the array. For example:
L could stand for "Left Shift" (shift elements to the left).
R could stand for "Right Shift" (shift elements to the right).

Simple Code Example:

function permute($str, $l, $r)
{
    if ($l == $r)
        echo $str. "\n";
    else {
        for ($i = $l; $i <= $r; $i++) {
            $str = swap($str, $l, $i);
            permute($str, $l + 1, $r);
            $str = swap($str, $l, $i);
        }
    }
}

To solve this permutation problem, I thought that need to demonstrate the keywords that are used many times in an array.

"K" and "N"
K refers to the value searched for and N refers to the size of the array. Moreover, the terms "K" and "N" in the context of an array can be referred to:

1. K and N as indices in an array (e.g., accessing elements at the K-th and N-th positions)
2. K and N as specific values within the array (e.g., looking for occurrences of K and N)
3. A problem involving K and N in arrays (such as sorting, searching, or comparisons)