LeetCode 170. Two Sum III - Data structure design (两数之和之三 - 数据结构设计)$
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
题目标签:Hash Table
题目让我们设计一个 两数之和的 class, 要有add(number) 和 find(value)功能。
建立HashMap,number 当作 key;number 出现的次数当作 value保存。
要注意的是,两数之和的 两数可以是相同的数字,出现两次。比如 2 + 2 = 4 也是可以的。
Java Solution:
Runtime beats 82.39%
完成日期:05/16/2017
关键词:HashMap
关键点:HashMap<number, occurrence>
1 class TwoSum 2 { 3 HashMap<Integer, Integer> map; 4 /** Initialize your data structure here. */ 5 public TwoSum() 6 { 7 map = new HashMap<>(); 8 } 9 10 /** Add the number to an internal data structure.. */ 11 public void add(int number) 12 { 13 map.put(number, map.getOrDefault(number, 0) + 1); 14 } 15 16 /** Find if there exists any pair of numbers which sum is equal to the value. */ 17 public boolean find(int value) 18 { 19 for(int num: map.keySet()) 20 { 21 int target = value - num; 22 23 if(num == target) 24 { 25 if(map.get(num) > 1) 26 return true; 27 } 28 else 29 { 30 if(map.containsKey(target)) 31 return true; 32 } 33 } 34 35 return false; 36 } 37 } 38 39 /** 40 * Your TwoSum object will be instantiated and called as such: 41 * TwoSum obj = new TwoSum(); 42 * obj.add(number); 43 * boolean param_2 = obj.find(value); 44 */
参考资料:N/A
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