import java.util.HashMap;
import java.util.Map;
public class TwoSum {
private Map<Integer, Integer> freq;
/**
* Initialize your data structure here.
*/
public TwoSum() {
freq = new HashMap<>();
}
/**
* Add the number to an internal data structure..
*/
public void add(int number) {
// 向数据结构添加一个数 number
freq.put(number, freq.getOrDefault(number, 0) + 1);
}
/**
* Find if there exists any pair of numbers which sum is equal to the value.
*/
public boolean find(int value) {
// 这里需要考虑两种特殊情况：a + a = value 和 a + b = value
for (Integer num : freq.keySet()) {
int rest = value - num;
// 情况 1：a + a = value 的时候，频数要严格大于 1
if (rest == num && freq.get(rest) > 1) {
return true;
}
// 情况 2：a + b = value
if (rest != num && freq.containsKey(rest)) {
return true;
}
}
return false;
}
}
