留言区没有人讨论课后题，我抛砖引玉下。注释就像文中所说，准确、必要和清晰最重要，也就是说在不同的团队同一段代码的注释会不同，因为团队能力不同。这里我试着用比较完整的方式做一段注释，如果团队能力好，一些部分是可以省略的

import java.util.HashMap;
import java.util.Map;

class TwoSumSolution {
    /**
     * Given an array of integers, return indices of the two numbers
     * such that they add up to a specific target.
     */

    public int[] twoSum(int[] nums, int target) {
        // init a map storing number and its index relation
        Map<Integer, Integer> map = new HashMap<>();

        for (int i = 0; i < nums.length; i++) {
            // calculate the complement of current number
            int complement = target - nums[i];
            // if map contains the complement, return complement directly, else update map with current number
            if (map.containsKey(complement)) {
                return new int[] { map.get(complement), i };
            }
            map.put(nums[i], i);
        }
        
        // if the sum of any two numbers is not equal to the specific target, throw illegal argument exception
        throw new IllegalArgumentException("No two sum solution");
    }
}