"content":"<p>Given a <strong>multi-dimensional</strong> array <code>arr</code> and a depth <code>n</code>, return a <strong>flattened</strong> version of that array.</p>\n\n<p>A <strong>multi-dimensional</strong> array is a recursive data structure that contains integers or other <strong>multi-dimensional</strong> arrays.</p>\n\n<p>A <strong>flattened</strong> array is a version of that array with some or all of the sub-arrays removed and replaced with the actual elements in that sub-array. This flattening operation should only be done if the current depth of nesting is less than <code>n</code>. The depth of the elements in the first array are considered to be <code>0</code>.</p>\n\n<p>Please solve it without the built-in <code>Array.flat</code> method.</p>\n\n<p> </p>\n<p><strong class=\"example\">Example 1:</strong></p>\n\n<pre>\n<strong>Input</strong>\narr = [1, 2, 3, [4, 5, 6], [7, 8, [9, 10, 11], 12], [13, 14, 15]]\nn = 0\n<strong>Output</strong>\n[1, 2, 3, [4, 5, 6], [7, 8, [9, 10, 11], 12], [13, 14, 15]]\n\n<strong>Explanation</strong>\nPassing a depth of n=0 will always result in the original array. This is because the smallest possible depth of a subarray (0) is not less than n=0. Thus, no subarray should be flattened. </pre>\n\n<p><strong class=\"example\">Example 2:</strong></p>\n\n<pre>\n<strong>Input</strong>\narr = [1, 2, 3, [4, 5, 6], [7, 8, [9, 10, 11], 12], [13, 14, 15]]\nn = 1\n<strong>Output</strong>\n[1, 2, 3, 4, 5, 6, 7, 8, [9, 10, 11], 12, 13, 14, 15]\n\n<strong>Explanation</strong>\nThe subarrays starting with 4, 7, and 13 are all flattened. This is because their depth of 0 is less than 1. However [9, 10, 11] remains unflattened because its depth is 1.</pre>\n\n<p><strong class=\"example\">Example 3:</strong></p>\n\n<pre>\n<strong>Input</strong>\narr = [[1, 2, 3], [4, 5, 6], [7, 8, [9, 10, 11], 12], [13, 14, 15]]\nn = 2\n<strong>Output</strong>\n[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]\n\n<strong>Explanation</strong>\nThe maximum depth of any subarray is 1. Thus, all of them are flattened.</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>0 <= count of numbers in arr <= 10<sup>5</sup></code></li>\n\t<li><code>0 <= count of subarrays in arr <= 10<sup>5</sup></code></li>\n\t<li><code>maxDepth <= 1000</code></li>\n\t<li><code>-1000 <= each number <= 1000</code></li>\n\t<li><code><font face=\"monospace\">0 <= n <= 1000</font></code></li>\n</ul>\n",
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