# [Leetcode] Training day-005

You are given two strings `s`

and `t`

.

String `t`

is generated by random shuffling string `s`

and then add one more letter at a random position.

Return the letter that was added to `t`

.

**Constraints:**

`0 <= s.length <= 1000`

`t.length == s.length + 1`

`s`

and`t`

consist of lower-case English letters.

參考：Link

There is a list of sorted integers from 1 to *n*. Starting from left to right, remove the first number and every other number afterward until you reach the end of the list.

Repeat the previous step again, but this time from right to left, remove the right most number and every other number from the remaining numbers.

We keep repeating the steps again, alternating left to right and right to left, until a single number remains.

Find the last number that remains starting with a list of length *n*.

參考：Link