170 Two Sum III - Data structure design
05.17
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.
Example 1:
add(1); add(3); add(5);
find(4) -> true
find(7) -> false
Example 2:
add(3); add(1); add(2);
find(3) -> true
find(6) -> false
class TwoSum {
/** Initialize your data structure here. */
public TwoSum() {
}
/** Add the number to an internal data structure.. */
public void add(int number) {
}
/** Find if there exists any pair of numbers which sum is equal to the value. */
public boolean find(int value) {
}
}
/**
* Your TwoSum object will be instantiated and called as such:
* TwoSum obj = new TwoSum();
* obj.add(number);
* boolean param_2 = obj.find(value);
*/
use hashmap and then loop through all the entries in the map
注意这个地方的逻辑
还有就是注意这个可以用个hashset 存一下出现的数字
- [x] ```
if((key == diff && map.get(key) > 1 )||(key != diff && map.containsKey(diff))) {
```return true; }
class TwoSum {
/** Initialize your data structure here. */
private Map<Integer, Integer> map;
public TwoSum() {
map = new HashMap<>();
}
/** 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 (Map.Entry<Integer, Integer> entry : map.entrySet()) {
int key = entry.getKey();
int diff = value - key;
if((key == diff && map.get(key) > 1 )||(key != diff && map.containsKey(diff))) {
return true;
}
}
return false;
}
}
/**
* Your TwoSum object will be instantiated and called as such:
* TwoSum obj = new TwoSum();
* obj.add(number);
* boolean param_2 = obj.find(value);
*/