1. Title
89. Gray Code
2. Http address
https://leetcode.com/problems/gray-code/?tab=Description
3. The question
The gray code is a binary numeral system where two successive values differ in only one bit.
Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray code. A gray code sequence must begin with 0.
For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:
00 - 0
01 - 1
11 - 3
10 - 2
Note:
For a given n, a gray code sequence is not uniquely defined.
For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.
For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.
4 My code(AC)
public class Solution { public List<Integer> grayCode(int n) { List<Integer> reList = new ArrayList<Integer>(); reList.add(0); if (n <= 0) { return reList; } int cur = 0; String curBinaryStr = Integer.toBinaryString(cur); n = 1 << n; curBinaryStr = "0" + curBinaryStr; for (int i = 1; i < n ; i++) { int len = curBinaryStr.length(); for (int j = len -1; j >= 0; j--) { String newStr = curBinaryStr.substring(0, j); if (curBinaryStr.charAt(j) == '1') { newStr += "0"; } else { newStr += "1"; } newStr += curBinaryStr.substring(j + 1, len); int newInt = Integer.valueOf(newStr, 2); if (!reList.contains(newInt)) { reList.add(newInt); cur = newInt; curBinaryStr = Integer.toBinaryString(cur); curBinaryStr = "0" + curBinaryStr; break; } } } return reList; } }