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44 lines
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44 lines
2.1 KiB
HTML
<p>You are given an integer <code>n</code> and an array of <strong>unique</strong> integers <code>blacklist</code>. Design an algorithm to pick a random integer in the range <code>[0, n - 1]</code> that is <strong>not</strong> in <code>blacklist</code>. Any integer that is in the mentioned range and not in <code>blacklist</code> should be <strong>equally likely</strong> to be returned.</p>
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<p>Optimize your algorithm such that it minimizes the number of calls to the <strong>built-in</strong> random function of your language.</p>
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<p>Implement the <code>Solution</code> class:</p>
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<ul>
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<li><code>Solution(int n, int[] blacklist)</code> Initializes the object with the integer <code>n</code> and the blacklisted integers <code>blacklist</code>.</li>
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<li><code>int pick()</code> Returns a random integer in the range <code>[0, n - 1]</code> and not in <code>blacklist</code>.</li>
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</ul>
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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>
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["Solution", "pick", "pick", "pick", "pick", "pick", "pick", "pick"]
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[[7, [2, 3, 5]], [], [], [], [], [], [], []]
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<strong>Output</strong>
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[null, 0, 4, 1, 6, 1, 0, 4]
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<strong>Explanation</strong>
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Solution solution = new Solution(7, [2, 3, 5]);
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solution.pick(); // return 0, any integer from [0,1,4,6] should be ok. Note that for every call of pick,
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// 0, 1, 4, and 6 must be equally likely to be returned (i.e., with probability 1/4).
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solution.pick(); // return 4
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solution.pick(); // return 1
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solution.pick(); // return 6
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solution.pick(); // return 1
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solution.pick(); // return 0
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solution.pick(); // return 4
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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>1 <= n <= 10<sup>9</sup></code></li>
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<li><code>0 <= blacklist.length <- min(10<sup>5</sup>, n - 1)</code></li>
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<li><code>0 <= blacklist[i] < n</code></li>
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<li>All the values of <code>blacklist</code> are <strong>unique</strong>.</li>
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<li>At most <code>2 * 10<sup>4</sup></code> calls will be made to <code>pick</code>.</li>
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</ul>
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