[LC] 170. Two Sum III - Data structure design

Posted 2020-11-26 xuanlu

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.

Example 1:

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

Example 2:

add(3); add(1); add(2);
find(3) -> true
find(6) -> false

class TwoSum {

    /** Initialize your data structure here. */
    private Map<Integer, Integer> map;
    public TwoSum() {
        map = new HashMap<>();
    }
    
    /** Add the number to an internal data structure.. */
    // O(1)
    public void add(int number) {
        map.put(number, map.getOrDefault(number, 0) + 1);
    }
    
    /** Find if there exists any pair of numbers which sum is equal to the value. */
    // O(N)
    public boolean find(int value) {
        for(int num : map.keySet()) {
            int target = value - num;
            if (map.containsKey(target) && (target != num || map.get(target) > 1)) {
                return true;
            }
        }
        return false;
    }
}

/**
 * Your TwoSum object will be instantiated and called as such:
 * TwoSum obj = new TwoSum();
 * obj.add(number);
 * boolean param_2 = obj.find(value);
 */