mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
synced 2025-01-10 18:48:13 +08:00
44 lines
2.1 KiB
HTML
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>
|
|
|
|
<p>Optimize your algorithm such that it minimizes the number of calls to the <strong>built-in</strong> random function of your language.</p>
|
|
|
|
<p>Implement the <code>Solution</code> class:</p>
|
|
|
|
<ul>
|
|
<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>
|
|
<li><code>int pick()</code> Returns a random integer in the range <code>[0, n - 1]</code> and not in <code>blacklist</code>.</li>
|
|
</ul>
|
|
|
|
<p> </p>
|
|
<p><strong class="example">Example 1:</strong></p>
|
|
|
|
<pre>
|
|
<strong>Input</strong>
|
|
["Solution", "pick", "pick", "pick", "pick", "pick", "pick", "pick"]
|
|
[[7, [2, 3, 5]], [], [], [], [], [], [], []]
|
|
<strong>Output</strong>
|
|
[null, 0, 4, 1, 6, 1, 0, 4]
|
|
|
|
<strong>Explanation</strong>
|
|
Solution solution = new Solution(7, [2, 3, 5]);
|
|
solution.pick(); // return 0, any integer from [0,1,4,6] should be ok. Note that for every call of pick,
|
|
// 0, 1, 4, and 6 must be equally likely to be returned (i.e., with probability 1/4).
|
|
solution.pick(); // return 4
|
|
solution.pick(); // return 1
|
|
solution.pick(); // return 6
|
|
solution.pick(); // return 1
|
|
solution.pick(); // return 0
|
|
solution.pick(); // return 4
|
|
</pre>
|
|
|
|
<p> </p>
|
|
<p><strong>Constraints:</strong></p>
|
|
|
|
<ul>
|
|
<li><code>1 <= n <= 10<sup>9</sup></code></li>
|
|
<li><code>0 <= blacklist.length <= min(10<sup>5</sup>, n - 1)</code></li>
|
|
<li><code>0 <= blacklist[i] < n</code></li>
|
|
<li>All the values of <code>blacklist</code> are <strong>unique</strong>.</li>
|
|
<li>At most <code>2 * 10<sup>4</sup></code> calls will be made to <code>pick</code>.</li>
|
|
</ul>
|