哈希表
class Solution {
public int[] twoSum(int[] nums, int target) {
HashMap<Integer, Integer> map = new HashMap<>();
for(int i = 0; i < nums.length; i++){
if(map.containsKey(target - nums[i])){
return new int[]{map.get(target - nums[i]), i};
}
map.put(nums[i], i);
}
return new int[0];
}
}