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42 lines
1.4 KiB
HTML
42 lines
1.4 KiB
HTML
<p>You have a pointer at index <code>0</code> in an array of size <code>arrLen</code>. At each step, you can move 1 position to the left, 1 position to the right in the array, or stay in the same place (The pointer should not be placed outside the array at any time).</p>
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<p>Given two integers <code>steps</code> and <code>arrLen</code>, return the number of ways such that your pointer still at index <code>0</code> after <strong>exactly</strong> <code>steps</code> steps. Since the answer may be too large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>
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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> steps = 3, arrLen = 2
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<strong>Output:</strong> 4
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<strong>Explanation: </strong>There are 4 differents ways to stay at index 0 after 3 steps.
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Right, Left, Stay
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Stay, Right, Left
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Right, Stay, Left
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Stay, Stay, Stay
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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> steps = 2, arrLen = 4
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> There are 2 differents ways to stay at index 0 after 2 steps
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Right, Left
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Stay, Stay
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</pre>
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<p><strong>Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> steps = 4, arrLen = 2
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<strong>Output:</strong> 8
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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 <= steps <= 500</code></li>
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<li><code>1 <= arrLen <= 10<sup>6</sup></code></li>
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</ul>
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