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62 lines
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62 lines
2.5 KiB
HTML
<p>You are playing a game involving a <strong>circular</strong> array of non-zero integers <code>nums</code>. Each <code>nums[i]</code> denotes the number of indices forward/backward you must move if you are located at index <code>i</code>:</p>
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<ul>
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<li>If <code>nums[i]</code> is positive, move <code>nums[i]</code> steps <strong>forward</strong>, and</li>
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<li>If <code>nums[i]</code> is negative, move <code>nums[i]</code> steps <strong>backward</strong>.</li>
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</ul>
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<p>Since the array is <strong>circular</strong>, you may assume that moving forward from the last element puts you on the first element, and moving backwards from the first element puts you on the last element.</p>
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<p>A <strong>cycle</strong> in the array consists of a sequence of indices <code>seq</code> of length <code>k</code> where:</p>
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<ul>
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<li>Following the movement rules above results in the repeating index sequence <code>seq[0] -> seq[1] -> ... -> seq[k - 1] -> seq[0] -> ...</code></li>
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<li>Every <code>nums[seq[j]]</code> is either <strong>all positive</strong> or <strong>all negative</strong>.</li>
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<li><code>k > 1</code></li>
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</ul>
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<p>Return <code>true</code><em> if there is a <strong>cycle</strong> in </em><code>nums</code><em>, or </em><code>false</code><em> otherwise</em>.</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> nums = [2,-1,1,2,2]
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<strong>Output:</strong> true
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<strong>Explanation:</strong>
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There is a cycle from index 0 -> 2 -> 3 -> 0 -> ...
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The cycle's length is 3.
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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> nums = [-1,2]
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<strong>Output:</strong> false
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<strong>Explanation:</strong>
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The sequence from index 1 -> 1 -> 1 -> ... is not a cycle because the sequence's length is 1.
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By definition the sequence's length must be strictly greater than 1 to be a cycle.
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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> nums = [-2,1,-1,-2,-2]
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<strong>Output:</strong> false
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<strong>Explanation:</strong>
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The sequence from index 1 -> 2 -> 1 -> ... is not a cycle because nums[1] is positive, but nums[2] is negative.
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Every nums[seq[j]] must be either all positive or all negative.
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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 <= nums.length <= 5000</code></li>
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<li><code>-1000 <= nums[i] <= 1000</code></li>
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<li><code>nums[i] != 0</code></li>
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</ul>
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<p> </p>
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<p><strong>Follow up:</strong> Could you solve it in <code>O(n)</code> time complexity and <code>O(1)</code> extra space complexity?</p>
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