170. Two Sum III - Data structure design

Posted 2020-08-09 Machelsky

Design and implement a TwoSum class. It should support the following operations: add and find.

add - Add the number to an internal data structure.
find - Find if there exists any pair of numbers which sum is equal to the value.

For example,

add(1); add(3); add(5);
find(4) -> true
find(7) -> false

思路：思路跟two sum差不多，用hashmap存读到的数，value存个数。find只要遍历map然后检查是不是有被减数，如果被减数等于减数，检查个数即可。

public class TwoSum {
    Map<Integer,Integer> res=new HashMap<Integer,Integer>();
    // Add the number to an internal data structure.
    public void add(int number) {
        if(res.containsKey(number))
        {
            res.put(number,res.get(number)+1);
        }
        else
        {
            res.put(number,1);
        }
    }

    // Find if there exists any pair of numbers which sum is equal to the value.
    public boolean find(int value) {
        if(res.isEmpty())
        {
            return false;
        }
        for(int number:res.keySet())
        {
            if(res.containsKey(value-number))
            {
               if(value-number==number)
               {
                   if(res.get(number)>=2)
                   {
                   return true;
                   }
               }
               else
               {
                   return true;
               }
            }
        }
        return false;
        
    }
}


// Your TwoSum object will be instantiated and called as such:
// TwoSum twoSum = new TwoSum();
// twoSum.add(number);
// twoSum.find(value);