LeetCode089 Gray Code

详细见：leetcode.com/problems/gray-code

Java Solution:
github

package leetcode;

import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;

/*
* 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.
*/

public class P089_GrayCode {
public static void main(String[] args) {
List<Integer> ans = new Solution().grayCode(0);
tools.Utils.B_打印List_Integer(ans);;
}
/*
* WA了一个输入为0
* AC
* 5 ms
*/
static class Solution {
HashSet<Integer> set = new HashSet<>();
List<Integer> ans = new LinkedList<Integer>();
int[] arr = null;
int count = 0, n = 0, set_max_size = 0;
boolean isDone = false;
public List<Integer> grayCode(int n) {
if (n < 0) {
return ans;
}
this.n = n;
set_max_size = 1 << n;
arr = new int
;
ans.add(0);
set.add(0);
search();
return ans;
}
private void search() {
if (set.size() == set_max_size) {
isDone = true;
return;
}
if (isDone) {
return;
}
for (int i = n - 1;! isDone && i > -1; i --) {
arr[i] = arr[i] == 0 ? 1 : 0;
if (add()) {
search();
}
arr[i] = arr[i] == 0 ? 1 : 0;
}
}
private boolean add() {
int val = 0;
for (int i = 0; i != arr.length; i ++) {
val = val * 2 + arr[i];
}
if (! set.contains(val)) {
ans.add(val);
set.add(val);
return true;
} else {
return false;
}
}
}
}


C Solution:
github

/*
url: leetcode.com/problems/gray-code
AC 3ms 26.92%
*/

#include <stdio.h>
#include <stdlib.h>

int* grayCode(int n, int* rn) {
int* a = NULL, ai = 0;
int* r = NULL, ri = 0, v = 0, *t = NULL;
int an = 1 << n;
if (n < 1) {
*rn = 1;
a = (int*) malloc(sizeof(int) * 1);
a[0] = 0;
return a;
}
a = (int*) malloc(sizeof(int) * an);
r = (int*) malloc(sizeof(int) * n);
t = (int*) malloc(sizeof(int) * n);
v = 2;
for (ri = n-1; ri > -1; ri --) {
r[ri] = v;
t[ri] = -v/2;
v <<= 1;
}
while (1) {
v = 0;
for (ri = 0; ri < n; ri ++)
if (t[ri] > 0) v += r[ri]/2;
a[ai ++] = v;
if (ai == an) break;
for (ri = 0; ri < n; ri ++) {
if (t[ri] > 0) {
t[ri] --;
if (t[ri] == 0) t[ri] = -r[ri];
} else {
t[ri] ++;
if (t[ri] == 0) t[ri] = r[ri];
}
}
}
*rn = an;
return a;
}

int main() {
int n = 3;
int rn = 0;
int* a = grayCode(n, &rn);
int i = 0;
for (i = 0; i < rn; i ++)
printf("%d\r\n", a[i]);
free(a);
return 0;
}

Python Solution:
github

#coding=utf-8

'''
url: leetcode.com/problems/gray-code
@author: zxwtry
@email: zxwtry@qq.com
@date: 2017年4月22日
@details: Solution: 62ms 26.96%
'''

class Solution(object):
def grayCode(self, n):
"""
:type n: int
:rtype: List[int]
"""
s, r, v, a = [0]*n, [0]*n, 2, []
for i in range(n-1, -1, -1):
s[i] = v
r[i] = -v / 2
v *= 2
for v in range(1 << n):
val = 0
for i in range(n):
val = val * 2 + (0 if r[i]<0 else 1)
a.append(val)
for i in range(n):
if r[i] > 0:
r[i] -= 1
if r[i] == 0: r[i] = -s[i]
else:
r[i] += 1
if r[i] == 0: r[i] = s[i]
return a

if __name__ == "__main__":
print(Solution().grayCode(3))