标签：
原题链接在这里：https://leetcode.com/problems/two-sum-iii-data-structure-design/
题目：
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
题解：
与Two Sum类似.
简历HashMap保存key 和 key的frequency. find value时把HashMap的每一个key当成num1, 来查找HashMap是否有另一个value-num1的key.
num1 = value - num1时，检查num1的frequency是否大于1.
Time Complexity: add O(1). find O(n). Space: O(n).
AC Java:
1 public class TwoSum { 2 private HashMap<Integer, Integer> hm = new HashMap<Integer, Integer>(); 3 // Add the number to an internal data structure. 4 public void add(int number) { 5 if(!hm.containsKey(number)){ 6 hm.put(number, 1); 7 }else{ 8 hm.put(number, hm.get(number)+1); 9 } 10 } 11 12 // Find if there exists any pair of numbers which sum is equal to the value. 13 public boolean find(int value) { 14 for(Map.Entry<Integer, Integer> entry : hm.entrySet()){ 15 int num1 = entry.getKey(); 16 int num2 = value - num1; 17 if(hm.containsKey(num2) && (hm.get(num2) > 1 || num2 != num1)){ 18 return true; 19 } 20 } 21 return false; 22 } 23 } 24 25 26 // Your TwoSum object will be instantiated and called as such: 27 // TwoSum twoSum = new TwoSum(); 28 // twoSum.add(number); 29 // twoSum.find(value);
LeetCode Two Sum III - Data structure design
标签：
原文地址：http://www.cnblogs.com/Dylan-Java-NYC/p/5324746.html
