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34 lines
1.7 KiB
HTML
34 lines
1.7 KiB
HTML
<p>Implement a SnapshotArray that supports the following interface:</p>
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<ul>
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<li><code>SnapshotArray(int length)</code> initializes an array-like data structure with the given length. <strong>Initially, each element equals 0</strong>.</li>
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<li><code>void set(index, val)</code> sets the element at the given <code>index</code> to be equal to <code>val</code>.</li>
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<li><code>int snap()</code> takes a snapshot of the array and returns the <code>snap_id</code>: the total number of times we called <code>snap()</code> minus <code>1</code>.</li>
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<li><code>int get(index, snap_id)</code> returns the value at the given <code>index</code>, at the time we took the snapshot with the given <code>snap_id</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> ["SnapshotArray","set","snap","set","get"]
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[[3],[0,5],[],[0,6],[0,0]]
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<strong>Output:</strong> [null,null,0,null,5]
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<strong>Explanation: </strong>
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SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3
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snapshotArr.set(0,5); // Set array[0] = 5
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snapshotArr.snap(); // Take a snapshot, return snap_id = 0
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snapshotArr.set(0,6);
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snapshotArr.get(0,0); // Get the value of array[0] with snap_id = 0, return 5</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 <= length <= 50000</code></li>
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<li>At most <code>50000</code> calls will be made to <code>set</code>, <code>snap</code>, and <code>get</code>.</li>
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<li><code>0 <= index < length</code></li>
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<li><code>0 <= snap_id < </code>(the total number of times we call <code>snap()</code>)</li>
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<li><code>0 <= val <= 10^9</code></li>
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</ul>
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