# Leetcode 89 - Gray code

Note:

• Kinda hard to find the pattern, so DFS all the way.
• Use  num ^ 1 << i to flip bits.
• Use set to check if we’ve use a num before.
• The longest length of num is n bits.

Question:

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:

Code: