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47 lines
2.2 KiB
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47 lines
2.2 KiB
HTML
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<p>Given an array <code>arr</code> that represents a permutation of numbers from <code>1</code> to <code>n</code>.</p>
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<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>
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<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>
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<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>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> arr = [3,5,1,2,4], m = 1
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<strong>Output:</strong> 4
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<strong>Explanation:</strong>
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Step 1: "00<u>1</u>00", groups: ["1"]
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Step 2: "0010<u>1</u>", groups: ["1", "1"]
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Step 3: "<u>1</u>0101", groups: ["1", "1", "1"]
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Step 4: "1<u>1</u>101", groups: ["111", "1"]
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Step 5: "111<u>1</u>1", groups: ["11111"]
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The latest step at which there exists a group of size 1 is step 4.
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> arr = [3,1,5,4,2], m = 2
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<strong>Output:</strong> -1
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<strong>Explanation:</strong>
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Step 1: "00<u>1</u>00", groups: ["1"]
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Step 2: "<u>1</u>0100", groups: ["1", "1"]
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Step 3: "1010<u>1</u>", groups: ["1", "1", "1"]
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Step 4: "101<u>1</u>1", groups: ["1", "111"]
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Step 5: "1<u>1</u>111", groups: ["11111"]
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No group of size 2 exists during any step.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>n == arr.length</code></li>
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<li><code>1 <= m <= n <= 10<sup>5</sup></code></li>
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<li><code>1 <= arr[i] <= n</code></li>
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<li>All integers in <code>arr</code> are <strong>distinct</strong>.</li>
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</ul>
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