不懂的题目：

https://leetcode.com/problems/find-k-pairs-with-smallest-sums/discuss/84551

https://leetcode.com/problems/container-with-most-water/description/

https://leetcode.com/problems/best-meeting-point/description/

=====

https://leetcode.com/problems/copy-list-with-random-pointer/description/

答案参考如下：

https://www.jiuzhang.com/solution/copy-list-with-random-pointer/

char - > num:

• Character.getNumericValue(c)
• c - '0'

num -> char

• char c = (char) (num + '0'); explanation

ASCII Table

大写字母从65 到 90

小写字母从97 到 122

https://www.cs.cmu.edu/~pattis/15-1XX/common/handouts/ascii.html

直接造一个list，Arrays.asList(nums[i], nums[left], nums[right])，不需要手动放入每一个element

list -> array

List<String> res = new LinkedList<>();

res.toArray(new String[0]);