1146. Snapshot Array

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1146. Snapshot Array

Description

Implement a SnapshotArray that supports the following interface:

  • SnapshotArray(int length) initializes an array-like data structure with the given length. Initially, each element equals 0 .
  • void set(index, val) sets the element at the given index to be equal to val.
  • int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1.
  • int get(index, snap_id) returns the value at the given index, at the time we took the snapshot with the given snap_id

Example 1:

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Input: ["SnapshotArray","set","snap","set","get"]
[[3],[0,5],[],[0,6],[0,0]]
Output: [null,null,0,null,5]
Explanation:
SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3
snapshotArr.set(0,5);  // Set array[0] = 5
snapshotArr.snap();  // Take a snapshot, return snap_id = 0
snapshotArr.set(0,6);
snapshotArr.get(0,0);  // Get the value of array[0] with snap_id = 0, return 5

Constraints:

  • 1 <= length <= 5 * 10^4
  • 0 <= index < length
  • 0 <= val <= 10^9
  • 0 <= snap_id < (the total number of times we call snap())
  • At most 5 * 10^4 calls will be made to set, snap, and get.

Hints/Notes

Solution

Language: C++

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class SnapshotArray {
public:
    int curSnapId = 0;
    vector<map<int, int>> array;
    SnapshotArray(int length) {
        array.resize(length);
    }

    void set(int index, int val) {
        array[index][curSnapId] = val;
    }

    int snap() {
        return curSnapId++;
    }

    int get(int index, int snap_id) {
        if (array[index].empty() || array[index].begin()->first > snap_id) {
            return 0;
        }
        return prev(array[index].upper_bound(snap_id))->second;
    }
};

/**
 * Your SnapshotArray object will be instantiated and called as such:
 * SnapshotArray* obj = new SnapshotArray(length);
 * obj->set(index,val);
 * int param_2 = obj->snap();
 * int param_3 = obj->get(index,snap_id);
 */