LeetCode - Gray Code
Problem description
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.
Example 1:
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Input: 2
Output: [0,1,3,2]
Explanation:
00 - 0
01 - 1
11 - 3
10 - 2
For a given n, a gray code sequence may not be uniquely defined.
For example, [0,2,3,1] is also a valid gray code sequence.
00 - 0
10 - 2
11 - 3
01 - 1
Example 2:
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Input: 0
Output: [0]
Explanation: We define the gray code sequence to begin with 0.
A gray code sequence of n has size = 2n, which for n = 0 the size is 20 = 1.
Therefore, for n = 0 the gray code sequence is [0].
Analysis
we separates the 2 example, and we can know that we will add Math.pow(2,i) for every item in list and for every i.
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00 - 0
01 - 1
--------
11 - 3 = 1+2
10 - 2 = 0+2
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class Solution {
public List<Integer> grayCode(int n) {
List<Integer> res = new ArrayList<>();
double temp = 0;
res.add((int)temp);
for (int i = 0; i < n; i++){
int max = (int)Math.pow(2, i);
for (int j = res.size() - 1; j >= 0; j--){
res.add(res.get(j) + max);
}
}
return res;
}
}
What to improve
- if I can’t get the solution in one minute than I have to think from scratch.