✡ leetcode 170. Two Sum III - Data structure design 设计two sum模式 --------- java

时间:2024-08-11 23:35:26
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

设计一个two sum 的类。包含add和find两种操作方式。

1、使用HashMap和HashSet实现。

public class TwoSum {

    Map<Integer,Integer> map = new HashMap<Integer,Integer>();
Set<Integer> set = new HashSet<Integer>();
// Add the number to an internal data structure.
public void add(int number) {
if (set.contains(number)){
map.put(number, 2);
}else {
set.add(number);
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 num : set){
if (num == value - num){
if (map.get(num) == 2){
return true;
}
} else if (set.contains(value - num)){
return true;
}
}
return false;
}
} // Your TwoSum object will be instantiated and called as such:
// TwoSum twoSum = new TwoSum();
// twoSum.add(number);
// twoSum.find(value);

2、使用HashMap 和 List(也可以只使用一个HashMap,记录一或者2即可。)

public class TwoSum {

    private List<Integer> list = new ArrayList<Integer>();
private Map<Integer, Integer> 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);
list.add(number);
}
} // Find if there exists any pair of numbers which sum is equal to the value.
public boolean find(int value) {
for (int i = 0; i < list.size(); i++){
int num1 = list.get(i), num2 = value - num1;
if ((num1 == num2 && map.get(num1) > 1) || (num1 != num2 && map.containsKey(num2))) return true;
}
return false;
}
} // Your TwoSum object will be instantiated and called as such:
// TwoSum twoSum = new TwoSum();
// twoSum.add(number);
// twoSum.find(value);

3、为什么要使用一个List,因为在遍历操作的时候,List要比Map或者Set快得多,使用一个List可以用空间换取时间。