Two Sum III - Data structure design

题目

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

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

解析

思路

图解

代码

class TwoSum {
    private HashMap<Integer, Integer> map;
    private List<Integer> list;

    /** Initialize your data structure here. */
    public TwoSum() {
        map = new HashMap<>();
        list = new ArrayList<>();
    }

    /** Add the number to an internal data structure.. */
    public void add(int number) {
        if(!map.containsKey(number)){
            map.put(number, 1);
            list.add(number);
        }else{
            map.put(number, map.get(number)+1);
        }  
    }

    /** Find if there exists any pair of numbers which sum is equal to the value. */
    public boolean find(int value) {
        for(Integer num1 : list){
            int num2 = value - num1;
            if((num1 == num2 && map.get(num1)>1)||(num1 !=num2 && map.containsKey(num2))){
                return true;
            }
        }
       return false; 
    }
}