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38 lines
1.7 KiB
HTML
38 lines
1.7 KiB
HTML
<p>Design the <code>CombinationIterator</code> class:</p>
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<ul>
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<li><code>CombinationIterator(string characters, int combinationLength)</code> Initializes the object with a string <code>characters</code> of <strong>sorted distinct</strong> lowercase English letters and a number <code>combinationLength</code> as arguments.</li>
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<li><code>next()</code> Returns the next combination of length <code>combinationLength</code> in <strong>lexicographical order</strong>.</li>
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<li><code>hasNext()</code> Returns <code>true</code> if and only if there exists a next combination.</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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["CombinationIterator", "next", "hasNext", "next", "hasNext", "next", "hasNext"]
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[["abc", 2], [], [], [], [], [], []]
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<strong>Output</strong>
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[null, "ab", true, "ac", true, "bc", false]
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<strong>Explanation</strong>
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CombinationIterator itr = new CombinationIterator("abc", 2);
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itr.next(); // return "ab"
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itr.hasNext(); // return True
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itr.next(); // return "ac"
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itr.hasNext(); // return True
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itr.next(); // return "bc"
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itr.hasNext(); // return False
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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 <= combinationLength <= characters.length <= 15</code></li>
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<li>All the characters of <code>characters</code> are <strong>unique</strong>.</li>
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<li>At most <code>10<sup>4</sup></code> calls will be made to <code>next</code> and <code>hasNext</code>.</li>
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<li>It is guaranteed that all calls of the function <code>next</code> are valid.</li>
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</ul>
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