高频题（0）
1. visiting cities
输入red，blue分别为长度为n的int arr，以及bluecost
red和blue为i-1城到城的距离，bluecost为红线转蓝线的距离，蓝转红无距离。
输出0号红站到1.2...n城的最短距离
例子：red=[5,5,5]，blue=[3,3,3]，bluecost=3，那么输出[0,5,9,12]
解释：0到0是0，0到1最近的是直接红线=5，0到2是转蓝（3+3）到1城，继续走蓝到2城（+3）
总共=9，0到3是3+3+3+3=12
2. Count Subarrays with Sum Divisible by K
Given an integer array nums and an integer k, return the number of non-empty subarrays that have a sum divisible by k.
A subarray is a contiguous part of an array.
Example 1:
Input: nums = [4,5,0,-2,-3,1], k = 5 Output: 7 Explanation: There are 7 subarrays with a sum divisible by k = 5: [4, 5, 0, -2, -3, 1], [5], [5, 0], [5, 0, -2, -3], [0], [0, -2, -3], [-2, -3]
Example 2:
Input: nums = [5], k = 9 Output: 0
Constraints:
- 1 <= nums.length <= 3 * 104
- -104 <= nums[i] <= 104
- 2 <= k <= 104
3. Lexicographical Numbers Ordering
Given an integer n, return all the numbers in the range [1, n] sorted in lexicographical order.
You must write an algorithm that runs in O(n) time and uses O(1) extra space.
Example 1:
Input: n = 13 Output: [1,10,11,12,13,2,3,4,5,6,7,8,9]
Example 2:
Input: n = 2 Output: [1,2]
Constraints:
- 1 <= n <= 5 * 104
4. Generating n-bit Gray Code Sequence
An n-bit gray code sequence is a sequence of 2n integers where:
- Every integer is in the inclusive range [0, 2n - 1],
- The first integer is 0,
- An integer appears no more than once in the sequence,
- The binary representation of every pair of adjacent integers differs by exactly one bit, and
- The binary representation of the first and last integers differs by exactly one bit.
Given an integer n, return any valid n-bit gray code sequence.
Example 1:
Input: n = 2 Output: [0,1,3,2] Explanation: The binary representation of [0,1,3,2] is [00,01,11,10]. - 00 and 01 differ by one bit - 01 and 11 differ by one bit - 11 and 10 differ by one bit - 10 and 00 differ by one bit [0,2,3,1] is also a valid gray code sequence, whose binary representation is [00,10,11,01]. - 00 and 10 differ by one bit - 10 and 11 differ by one bit - 11 and 01 differ by one bit - 01 and 00 differ by one bit
Example 2:
Input: n = 1 Output: [0,1]
Constraints:
- 1 <= n <= 16
5. Shortest Subarray with Sum at Least K
Given an integer array nums and an integer k, return the length of the shortest non-empty subarray of nums with a sum of at least k. If there is no such subarray, return -1.
A subarray is a contiguous part of an array.
Example 1:
Input: nums = [1], k = 1 Output: 1
Example 2:
Input: nums = [1,2], k = 4 Output: -1
Example 3:
Input: nums = [2,-1,2], k = 3 Output: 3
Constraints:
- 1 <= nums.length <= 105
- -105 <= nums[i] <= 105
- 1 <= k <= 109
