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"title": "Find Latest Group of Size M",
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"content": "<p>Given an array <code>arr</code> that represents a permutation of numbers from <code>1</code> to <code>n</code>.</p>\n\n<p>You have a binary string of size <code>n</code> that initially has all its bits set to zero. At each step <code>i</code> (assuming both the binary string and <code>arr</code> are 1-indexed) from <code>1</code> to <code>n</code>, the bit at position <code>arr[i]</code> is set to <code>1</code>.</p>\n\n<p>You are also given an integer <code>m</code>. Find the latest step at which there exists a group of ones of length <code>m</code>. A group of ones is a contiguous substring of <code>1</code>'s such that it cannot be extended in either direction.</p>\n\n<p>Return <em>the latest step at which there exists a group of ones of length <strong>exactly</strong></em> <code>m</code>. <em>If no such group exists, return</em> <code>-1</code>.</p>\n\n<p> </p>\n<p><strong>Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> arr = [3,5,1,2,4], m = 1\n<strong>Output:</strong> 4\n<strong>Explanation:</strong> \nStep 1: "00<u>1</u>00", groups: ["1"]\nStep 2: "0010<u>1</u>", groups: ["1", "1"]\nStep 3: "<u>1</u>0101", groups: ["1", "1", "1"]\nStep 4: "1<u>1</u>101", groups: ["111", "1"]\nStep 5: "111<u>1</u>1", groups: ["11111"]\nThe latest step at which there exists a group of size 1 is step 4.\n</pre>\n\n<p><strong>Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> arr = [3,1,5,4,2], m = 2\n<strong>Output:</strong> -1\n<strong>Explanation:</strong> \nStep 1: "00<u>1</u>00", groups: ["1"]\nStep 2: "<u>1</u>0100", groups: ["1", "1"]\nStep 3: "1010<u>1</u>", groups: ["1", "1", "1"]\nStep 4: "101<u>1</u>1", groups: ["1", "111"]\nStep 5: "1<u>1</u>111", groups: ["11111"]\nNo group of size 2 exists during any step.\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>n == arr.length</code></li>\n\t<li><code>1 <= m <= n <= 10<sup>5</sup></code></li>\n\t<li><code>1 <= arr[i] <= n</code></li>\n\t<li>All integers in <code>arr</code> are <strong>distinct</strong>.</li>\n</ul>\n",
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"code": "class Solution(object):\n def findLatestStep(self, arr, m):\n \"\"\"\n :type arr: List[int]\n :type m: int\n :rtype: int\n \"\"\"\n ",
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"code": "# @param {Integer[]} arr\n# @param {Integer} m\n# @return {Integer}\ndef find_latest_step(arr, m)\n \nend",
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"code": "class Solution {\n\n /**\n * @param Integer[] $arr\n * @param Integer $m\n * @return Integer\n */\n function findLatestStep($arr, $m) {\n \n }\n}",
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"hints": [
"Since the problem asks for the latest step, can you start the searching from the end of arr?",
"Use a map to store the current “1” groups.",
"At each step (going backwards) you need to split one group and update the map."
],
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