Explain the core principle behind selection sort.

Selection sort is a simple comparison-based sorting algorithm. The core principle behind selection sort can be broken down into the following steps:

1. Find the Minimum Element: Start from the first element in the array and scan through the array to find the smallest (or largest, depending on the sorting order) element. This element is considered the "minimum element".

2. Swap: Once the minimum element is found, swap it with the first element of the array. Now, the first element of the array is the smallest element.

3. Iterate: Repeat the process for the rest of the array, i.e., find the minimum element in the remaining part of the array (excluding the already sorted part) and swap it with the first element of the remaining part.

4. Repeat Until Sorted: Continue this process until the entire array is sorted.

The key idea behind selection sort is that it maintains two subarrays within the given array: one subarray of already sorted elements (which is built up from left to right and is at the leftmost part of the array) and one subarray of the remaining elements that need to be sorted (the rightmost part of the array). The algorithm repeatedly selects the smallest (or largest) element from the unsorted subarray and moves it to the end of the sorted subarray. This process continues until the entire array is sorted.