Solved! Leetcode 1146. Snapshot Array

source: https://leetcode.com/problems/summary-ranges/description/

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:

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 * 104
0 <= index < length
0 <= val <= 109
0 <= snap_id < (the total number of times we call snap())
At most 5 * 104 calls will be made to set, snap, and get.

Solution

/**
 * 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);
 */

class SnapshotArray {
    private List<TreeMap<Integer, Integer>> snapshotList;
    private int nextSnapId = 0;
    public SnapshotArray(int length) {
        this.snapshotList = new ArrayList<>();
        for(int i=0;i<length;i++){
            this.snapshotList.add(new TreeMap<>());
            this.snapshotList.get(i).put(0, 0);
        }
    }

    public void set(int index, int val) {
        this.snapshotList.get(index).put(nextSnapId, val);
    }

    public int snap() {
        return this.nextSnapId++;
    }

    public int get(int index, int snap_id) {
        return this.snapshotList.get(index).floorEntry(snap_id).getValue();
    }
}

/**

* 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);

class SnapshotArray {

private List<TreeMap<Integer, Integer>> snapshotList;

private int nextSnapId = 0;

public SnapshotArray(int length) {

this.snapshotList = new ArrayList<>();

for(int i=0;i<length;i++){

this.snapshotList.add(new TreeMap<>());

this.snapshotList.get(i).put(0, 0);

}

public void set(int index, int val) {

this.snapshotList.get(index).put(nextSnapId, val);

}

public int snap() {

return this.nextSnapId++;

}

public int get(int index, int snap_id) {

return this.snapshotList.get(index).floorEntry(snap_id).getValue();

}

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