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60 lines
2.3 KiB
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60 lines
2.3 KiB
HTML
<p>You are given a <strong>0-indexed</strong> array of positive integers <code>w</code> where <code>w[i]</code> describes the <strong>weight</strong> of the <code>i<sup>th</sup></code> index.</p>
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<p>You need to implement the function <code>pickIndex()</code>, which <strong>randomly</strong> picks an index in the range <code>[0, w.length - 1]</code> (<strong>inclusive</strong>) and returns it. The <strong>probability</strong> of picking an index <code>i</code> is <code>w[i] / sum(w)</code>.</p>
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<ul>
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<li>For example, if <code>w = [1, 3]</code>, the probability of picking index <code>0</code> is <code>1 / (1 + 3) = 0.25</code> (i.e., <code>25%</code>), and the probability of picking index <code>1</code> is <code>3 / (1 + 3) = 0.75</code> (i.e., <code>75%</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","pickIndex"]
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[[[1]],[]]
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<strong>Output</strong>
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[null,0]
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<strong>Explanation</strong>
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Solution solution = new Solution([1]);
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solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w.
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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>
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["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
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[[[1,3]],[],[],[],[],[]]
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<strong>Output</strong>
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[null,1,1,1,1,0]
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<strong>Explanation</strong>
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Solution solution = new Solution([1, 3]);
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solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4.
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solution.pickIndex(); // return 1
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solution.pickIndex(); // return 1
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solution.pickIndex(); // return 1
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solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4.
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Since this is a randomization problem, multiple answers are allowed.
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All of the following outputs can be considered correct:
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[null,1,1,1,1,0]
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[null,1,1,1,1,1]
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[null,1,1,1,0,0]
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[null,1,1,1,0,1]
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[null,1,0,1,0,0]
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......
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and so on.
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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 <= w.length <= 10<sup>4</sup></code></li>
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<li><code>1 <= w[i] <= 10<sup>5</sup></code></li>
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<li><code>pickIndex</code> will be called at most <code>10<sup>4</sup></code> times.</li>
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</ul>
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