Thursday, September 3, 2020

LeetCode [1146] Snapshot Array

 1146. Snapshot Array

Medium

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 <= 50000
  • At most 50000 calls will be made to set, snap, and get.
  • 0 <= index < length
  • 0 <= snap_id < (the total number of times we call snap())
  • 0 <= val <= 10^9
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class SnapshotArray {
    TreeMap<Integer, Integer>[] ss;
    int snap_id = 0;
    public SnapshotArray(int length) {
        ss = new TreeMap[length];
        for(int i=0; i<length; ++i)
        {
            ss[i] = new TreeMap<Integer, Integer>();
            ss[i].put(0, 0);
        }
    }
    
    public void set(int index, int val) {
        ss[index].put(snap_id, val);
    }
    
    public int snap() {
        return snap_id++;
    }
    
    public int get(int index, int snap_id) {
        return ss[index].floorEntry(snap_id).getValue();
    }
    public static void main(String[] args) {
        System.out.println("Hi");
    }
}

/**
 * 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);
 */
at

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