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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
A simpler approach is to store each input into a hash table with the input as key and its count as value. To find if a pair sum exists, just iterate through the hash table in O(n) runtime. Make sure you are able to handle duplicates correctly.
1 public class TwoSum{ 2 //Firstly, we create a hashmap 3 Map<Integer, Integer> hm = new HashMap<>(); 4 5 public void add(int number){ 6 int count = hm.containsKey(number) ? hm.get(number): 0; 7 hm.put(number, count +1); 8 } 9 10 public boolean find(int value){ 11 //The Map.Entry interface enables you to work with a map entry 12 for(Map.Entry<Integer, Integer> entry: hm.entrySet()){ 13 int num = entry.getKey(); 14 int r = value - num; 15 if(r == num){ 16 // For duplicates, ensure there are at least two individual numbers 17 if(entry.getValue() >= 2) return true; 18 }else if(hm.containsKey(r)){ 19 return true; 20 } 21 } 22 return false; 23 } 24 }
Two Sum III - Data structure design(leetcode170）
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原文地址：http://www.cnblogs.com/caomeibaobaoguai/p/4873488.html
