89-m-Gray Code
2016-05-22 17:22
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求n位格雷码。
大概意思就是n bit的数,从0开始,下一个码从bit位层面来看只有1位相反,例如0x000的下一位是0x001,0x001的下一位可以是0x101, 0x011。
拿来一看觉得大概思路就是从最右边开始逐位^,找到第一个与之前不同的数然后加入result,那很显然还要个哈希表来存已知结果来比较,否则每次都要完全遍历数组检测在leet上必然超时。
写完ac后网搜了下,果然有套路,格雷码是有数学公式的,按照归纳出来的公式写代码就没几行,所以说计算机果然只是工具,精髓还是算法啊。自己的思路只是利用计算机的速度一个个对比,没有算法抽象,所以耗时是比较高的。
ac如下:
void grayCodeGenerate(int n, int *result, int *returnSize, char *table, int target, int *bingo) {
int cur = 1, tmp = 0;
for (int i = 0; i < n; i++) {
cur = 1;
cur = cur << i;
tmp = target ^ cur;
if (table[tmp] == 0) {
table[tmp] = 1;
result[*bingo] = tmp;
*bingo += 1;
grayCodeGenerate(n, result, returnSize, table, tmp, bingo);
}
}
}
int* grayCode(int n, int* returnSize) {
int count = 0, two = 1;
for (int i = 0; i < n; i++) {
count = two + count;
two *= 2;
}
count++;
*returnSize = count;
int *result = (int *)malloc(sizeof(int) * (*returnSize));
memset(result, 0, sizeof(int) * *returnSize);
char *table = (char *)malloc(*returnSize * sizeof(char));
memset(table, 0, sizeof(char) * *returnSize);
table[0] = 1;
int *bingo = (int *)malloc(sizeof(int));
*bingo = 1;
grayCodeGenerate(n, result, returnSize, table, 0, bingo);
return result;
}
大概意思就是n bit的数,从0开始,下一个码从bit位层面来看只有1位相反,例如0x000的下一位是0x001,0x001的下一位可以是0x101, 0x011。
拿来一看觉得大概思路就是从最右边开始逐位^,找到第一个与之前不同的数然后加入result,那很显然还要个哈希表来存已知结果来比较,否则每次都要完全遍历数组检测在leet上必然超时。
写完ac后网搜了下,果然有套路,格雷码是有数学公式的,按照归纳出来的公式写代码就没几行,所以说计算机果然只是工具,精髓还是算法啊。自己的思路只是利用计算机的速度一个个对比,没有算法抽象,所以耗时是比较高的。
ac如下:
void grayCodeGenerate(int n, int *result, int *returnSize, char *table, int target, int *bingo) {
int cur = 1, tmp = 0;
for (int i = 0; i < n; i++) {
cur = 1;
cur = cur << i;
tmp = target ^ cur;
if (table[tmp] == 0) {
table[tmp] = 1;
result[*bingo] = tmp;
*bingo += 1;
grayCodeGenerate(n, result, returnSize, table, tmp, bingo);
}
}
}
int* grayCode(int n, int* returnSize) {
int count = 0, two = 1;
for (int i = 0; i < n; i++) {
count = two + count;
two *= 2;
}
count++;
*returnSize = count;
int *result = (int *)malloc(sizeof(int) * (*returnSize));
memset(result, 0, sizeof(int) * *returnSize);
char *table = (char *)malloc(*returnSize * sizeof(char));
memset(table, 0, sizeof(char) * *returnSize);
table[0] = 1;
int *bingo = (int *)malloc(sizeof(int));
*bingo = 1;
grayCodeGenerate(n, result, returnSize, table, 0, bingo);
return result;
}
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