array questions

'array_map()' is a PHP function that applies a callback function to each element of one or more arrays. It returns an array containing the results. For example: `array_map('strtoupper', array('hello', 'world'));` would return `array('HELLO', 'WORLD')`. This function is useful for performing operations on array elements, such as transformations or formatting.

The `array_push()` function in PHP adds one or more elements to the end of an array. For example: `array_push($array, 'new_value');` will append 'new_value' to the end of `$array`. It can also accept multiple values: `array_push($array, 'value1', 'value2');`. This function is useful for dynamically adding items to arrays.

The `array_merge()` function in PHP combines multiple arrays into one. For example: `array_merge(array('a', 'b'), array('c', 'd'));` will result in `array('a', 'b', 'c', 'd')`. This function merges the arrays in the order they are passed, with the values of subsequent arrays appending to the first array. It is useful for aggregating data from multiple sources.

Binary search divides the search interval in half. Start with the middle element; if it matches the target, return it. Otherwise, adjust the search range to either the left or right half based on comparison. For example, searching for 4 in [1, 2, 3, 4, 5] returns index 3.

Use Kadane's Algorithm to find the maximum sum. Initialize the maximum sum and current sum as the first element, then iterate through the array updating these values. For example, for [1, -2, 3, 4, -1], the maximum subarray sum is 7.

Use a min-heap of size K to keep track of the K largest elements. For each element, if it is larger than the smallest element in the heap, replace the smallest. For example, in [3, 2, 1, 5, 6, 4], the 2nd largest element is 5.