170. Two Sum III - Data structure design

Description

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.

Constraints

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

Example 1

add(1); add(3); add(5);

find(4) -> true

find(7) -> false

Example 2

Solutions

Solution 1

/**
 * Time complexity : 
 * Space complexity : 
 */

class TwoSum {
    private Map<Integer, Integer> nums;

    /** Initialize your data structure here. */
    public TwoSum() {
        nums = new HashMap<Integer, Integer>();
    }
    
    /** Add the number to an internal data structure.. */
    public void add(int number) {
        nums.put(number, nums.getOrDefault(number, 0)+1);
    }
    
    /** Find if there exists any pair of numbers which 
        sum is equal to the value. */
    public boolean find(int value) {
        for(Integer n: nums.keySet()) {
            int complement = value - n;
            if(nums.containsKey(complement)) {
                if(complement == n && nums.get(complement) < 2) {
                    continue;
                }
                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);
 */

Follow up