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LeetCode 170. Two Sum III - Data Structure design

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Question

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. 

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

Explanation

和leetcode No.1一样，只是需要考虑的这里只能用一个不太需要维护的数据结构来存储，之前排序数组的那种方法就不可行了。同时要考虑计算frequency，会出现pair中两个数字是同一个的情况。

Code

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public class TwoSum {
    /** Initialize your data structure here. */
    HashMap<Integer, Integer> map;
    public TwoSum() {
        map = new HashMap<Integer, Integer>();
    }
    /** Add the number to an internal data structure.. */
    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(int key:map.keySet()){
            int left = value - key;
            if (left == key && map.get(key) > 1) {
                return true;
            } else if (left != key && map.containsKey(left)) {
                return true;
            }
        }
        return false;
    }
}