Leetcode981-timeBasedKey-ValueStore

Description

Create a timebased key-value store class TimeMap, that supports two operations.

1. set(string key, string value, int timestamp)

• Stores the key and value, along with the given timestamp.

1. get(string key, int timestamp)

• Returns a value such that set(key, value, timestamp_prev) was called previously, with timestamp_prev <= timestamp.
• If there are multiple such values, it returns the one with the largest timestamp_prev.
• If there are no values, it returns the empty string (“”).

  Example

  Example 1:

  Input: inputs = ["TimeMap","set","get","get","set","get","get"], inputs = [[],["foo","bar",1],["foo",1],["foo",3],["foo","bar2",4],["foo",4],["foo",5]]
  Output: [null,null,"bar","bar",null,"bar2","bar2"]
  Explanation:   
  TimeMap kv;   
  kv.set("foo", "bar", 1); // store the key "foo" and value "bar" along with timestamp = 1   
  kv.get("foo", 1);  // output "bar"   
  kv.get("foo", 3); // output "bar" since there is no value corresponding to foo at timestamp 3 and timestamp 2, then the only value is at timestamp 1 ie "bar"   
  kv.set("foo", "bar2", 4);   
  kv.get("foo", 4); // output "bar2"   
  kv.get("foo", 5); //output "bar2"   

  Example 2:

  Input: inputs = ["TimeMap","set","set","get","get","get","get","get"], inputs = [[],["love","high",10],["love","low",20],["love",5],["love",10],["love",15],["love",20],["love",25]]
  Output: [null,null,null,"","high","high","low","low"]

Note:

• All key/value strings are lowercase.
• All key/value strings have length in the range [1, 100]
• The timestamps for all TimeMap.set operations are strictly increasing.
• 1 <= timestamp <= 10^7
• TimeMap.set and TimeMap.get functions will be called a total of 120000 times (combined) per test case.

  Solution

  class TimeMap {
      class Node{
          String val;
          int times;
          public Node(String val, int times){
              this.val = val;
              this.times = times;
          }
      }
      
      HashMap<String, List<Node>> map;
      /** Initialize your data structure here. */
      public TimeMap() {
          map = new HashMap<String, List<Node>>();
      }
      
      public void set(String key, String value, int timestamp) {
          if (!map.containsKey(key)) map.put(key, new ArrayList<Node>());
          map.get(key).add(new Node(value, timestamp));
      }
      
      public String get(String key, int timestamp) {
          if (!map.containsKey(key)) return "";
          return binarySearch(map.get(key), timestamp);
      }
      
      private String binarySearch(List<Node> list, int timestamp){
          int left = 0;
          int right = list.size() - 1;
          while(left < right){
              int mid = (left + right) / 2;
              if (list.get(mid).times == timestamp) return list.get(mid).val;
              if (list.get(mid).times < timestamp){
                  if (list.get(mid + 1).times > timestamp) return list.get(mid).val;
                  left = mid + 1;
              }
              else right = mid - 1;
          }
          return list.get(left).times <= timestamp ? list.get(left).val : "";
      }
  }
  
  /**
   * Your TimeMap object will be instantiated and called as such:
   * TimeMap obj = new TimeMap();
   * obj.set(key,value,timestamp);
   * String param_2 = obj.get(key,timestamp);
   */

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