Two Sum III - Data structure design

Leetcode

題意：

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

解題思路：

主要運用到map.entry這個方法把所有key皆找出來，key value分別代表number 與count，程式碼如下：

public class TwoSum {

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

    // Find if there exists any pair of numbers which sum is equal to the value.
    public boolean find(int value) {
        for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
            int i = entry.getKey();
            int j = value - i;
            if (i == j && entry.getValue() > 1 || (i != j && map.containsKey(j))) {
                return true;
            }
        }
        return false;
    }
}