mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
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179 lines
17 KiB
JSON
179 lines
17 KiB
JSON
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"questionId": "754",
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"title": "Cracking the Safe",
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"content": "<p>There is a safe protected by a password. The password is a sequence of <code>n</code> digits where each digit can be in the range <code>[0, k - 1]</code>.</p>\n\n<p>The safe has a peculiar way of checking the password. When you enter in a sequence, it checks the <strong>most recent </strong><code>n</code><strong> digits</strong> that were entered each time you type a digit.</p>\n\n<ul>\n\t<li>For example, the correct password is <code>"345"</code> and you enter in <code>"012345"</code>:\n\n\t<ul>\n\t\t<li>After typing <code>0</code>, the most recent <code>3</code> digits is <code>"0"</code>, which is incorrect.</li>\n\t\t<li>After typing <code>1</code>, the most recent <code>3</code> digits is <code>"01"</code>, which is incorrect.</li>\n\t\t<li>After typing <code>2</code>, the most recent <code>3</code> digits is <code>"012"</code>, which is incorrect.</li>\n\t\t<li>After typing <code>3</code>, the most recent <code>3</code> digits is <code>"123"</code>, which is incorrect.</li>\n\t\t<li>After typing <code>4</code>, the most recent <code>3</code> digits is <code>"234"</code>, which is incorrect.</li>\n\t\t<li>After typing <code>5</code>, the most recent <code>3</code> digits is <code>"345"</code>, which is correct and the safe unlocks.</li>\n\t</ul>\n\t</li>\n</ul>\n\n<p>Return <em>any string of <strong>minimum length</strong> that will unlock the safe <strong>at some point</strong> of entering it</em>.</p>\n\n<p> </p>\n<p><strong class=\"example\">Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> n = 1, k = 2\n<strong>Output:</strong> "10"\n<strong>Explanation:</strong> The password is a single digit, so enter each digit. "01" would also unlock the safe.\n</pre>\n\n<p><strong class=\"example\">Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> n = 2, k = 2\n<strong>Output:</strong> "01100"\n<strong>Explanation:</strong> For each possible password:\n- "00" is typed in starting from the 4<sup>th</sup> digit.\n- "01" is typed in starting from the 1<sup>st</sup> digit.\n- "10" is typed in starting from the 3<sup>rd</sup> digit.\n- "11" is typed in starting from the 2<sup>nd</sup> digit.\nThus "01100" will unlock the safe. "10011", and "11001" would also unlock the safe.\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 <= n <= 4</code></li>\n\t<li><code>1 <= k <= 10</code></li>\n\t<li><code>1 <= k<sup>n</sup> <= 4096</code></li>\n</ul>\n",
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"difficulty": "Hard",
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"categoryTitle": "Algorithms",
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"name": "Depth-First Search",
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"name": "Eulerian Circuit",
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"code": "class Solution {\npublic:\n string crackSafe(int n, int k) {\n \n }\n};",
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"code": "class Solution(object):\n def crackSafe(self, n, k):\n \"\"\"\n :type n: int\n :type k: int\n :rtype: str\n \"\"\"\n ",
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"code": "# @param {Integer} n\n# @param {Integer} k\n# @return {String}\ndef crack_safe(n, k)\n \nend",
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"code": "impl Solution {\n pub fn crack_safe(n: i32, k: i32) -> String {\n \n }\n}",
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"code": "(define/contract (crack-safe n k)\n (-> exact-integer? exact-integer? string?)\n )",
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"code": "-spec crack_safe(N :: integer(), K :: integer()) -> unicode:unicode_binary().\ncrack_safe(N, K) ->\n .",
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"code": "defmodule Solution do\n @spec crack_safe(n :: integer, k :: integer) :: String.t\n def crack_safe(n, k) do\n \n end\nend",
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"We can think of this problem as the problem of finding an Euler path (a path visiting every edge exactly once) on the following graph: there are $$k^{n-1}$$ nodes with each node having $$k$$ edges. It turns out this graph always has an Eulerian circuit (path starting where it ends.)\r\n\r\nWe should visit each node in \"post-order\" so as to not get stuck in the graph prematurely."
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