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Commit 59f2351

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Add solution for Snapshot Array
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‎README.md

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@@ -31,6 +31,7 @@ Algorithm exercises from LeetCode implemented in Java v11.
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- Number of Good Pairs | [Problem](https://leetcode.com/problems/number-of-good-pairs) | [Solution](src/solutions/NumberOfGoodPairs.java)
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- Logger Rate Limiter | [Problem](https://leetcode.com/problems/logger-rate-limiter) | [Solution](src/solutions/Logger.java)
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- Unique Number of Occurrences | [Problem](https://leetcode.com/problems/unique-number-of-occurrences) | [Solution](src/solutions/UniqueNumberOfOccurrences.java)
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- Snapshot Array | [Problem](https://leetcode.com/problems/snapshot-array) | [Solution](src/solutions/SnapshotArray.java)
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### Stack
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- Min Stack | [Problem](https://leetcode.com/problems/min-stack) | [Solution](src/solutions/MinStack.java)

‎src/solutions/SnapshotArray.java

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package solutions;
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// [Problem] https://leetcode.com/problems/snapshot-array
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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// Hash table storing differences in each snapshot
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class SnapshotArray {
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List<Map<Integer, Integer>> diff;
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// O(m * n) space
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// where m = number of snapshots, n = number of changes in each snapshot
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public SnapshotArray(int length) {
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diff = new ArrayList<>();
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diff.add(new HashMap<>());
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}
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// O(1) time
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public void set(int index, int val) {
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diff.get(diff.size() - 1).put(index, val);
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}
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// O(1) time
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public int snap() {
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diff.add(new HashMap<>());
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return diff.size() - 2;
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}
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// O(n) time, where n = number of snapshots
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public int get(int index, int snapId) {
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for (int id = snapId; id >= 0; id--) {
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if (diff.get(id).containsKey(index)) {
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return diff.get(id).get(index);
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}
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}
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return 0;
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}
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public static void main(String[] args) {
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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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System.out.println(snapshotArr.snap()); // Take a snapshot, return snap_id = 0
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snapshotArr.set(0, 6);
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System.out.println(snapshotArr.get(0, 0)); // Get the value of array[0] with snap_id = 0, return 5
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}
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}

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