如何最有效地计算俄罗斯方块堆栈的高度轮廓? [英] How to compute the height profile of a Tetris stack most efficiently?
问题描述
我们得到了一个长度为height
的整数stack
数组. width
告诉我们,xs
的每个条目中最多设置了width
-最低位.
We're given an array of Integers stack
of length height
. The width
tells us that at most the width
-lowest bits in each entry of xs
are set.
计算长度为width
的数组profile
,使得profile[i] == max_i
带有max_i
的位置最大,而stack[max_i]
的第i
位被设置.
Compute an array profile
of length width
such that profile[i] == max_i
with: max_i
is maximal with stack[max_i]
having the i
-th bit set.
我怎样才能比下面更有效地实现这一目标?
How can I achieve this in a more efficient way than below?
目前,我浏览各列并分别检查每一位.
Currently I go over the columns and check each bit separately.
以下显示了我当前在Scala中的实现.但是请随意用其他语言(Java,C,C ++)给出答案,因为我主要对算法部分感兴趣(针对当前CPU进行了优化).
The following shows my current implementation in Scala. But feel free to give answers in other languages (Java, C, C++), as I am mainly interested in the algorithmic part (optimized for current CPUs).
Scala代码:
def tetrisProfile(stack: Array[Int]): Array[Int] = {
var col = 0
val profile = new Array[Int](width)
while(col < width){
var row = 0
var max = 0
while(row < height){
if(((stack(row) >> col) & 1) == 1)
max = row + 1
row += 1
}
profile(col) = max
col += 1
}
return profile
}
典型值
- 数组大小
height
为22 - 宽度
width
为10 - array size
height
is 22 - width
width
is 10
Typical values
当前结果:
original: 2.070s, 2.044s, 1.973s, 1.973s, 1.973s
maxihatop: 0.492s, 0.483s, 0.490s, 0.490s, 0.489s
推荐答案
我在C上编写了解决方案.希望您能够将算法移植到Java或Scala.
I wrote my solution on C. I hope, you will able port algorithm to Java or Scala.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define WIDTH 10
#define HEIGHT 22
// Convert (1 << n) to n for n == 0-10
static char bit2ndx[11] = {-1, 0, 1, 8, 2, 4, 9, 7, 3, 6, 5};
int *tetrisProfile(int *input) {
int row;
// allocate memory and set everything to -1 - default rc value,
// returned if no any result for this column
int *rc = (int *)malloc(WIDTH * sizeof(int));
memset(rc, ~0, WIDTH * sizeof(int));
// create bitset for columns for check
int testbits = (1 << WIDTH) - 1;
// Iterate rows from up to bottom, and while exist columns for check
for(row = HEIGHT - 1; row >= 0 && testbits != 0; row--) {
int rowtestbits = testbits & input[row];
while(rowtestbits != 0) {
// extract lowest bit_1 from bitset rowtestbits
int curbit = rowtestbits & -rowtestbits;
rc[bit2ndx[curbit % 11]] = row;
rowtestbits ^= curbit;
testbits ^= curbit;
}
}
return rc;
}
int stack[HEIGHT] = {0x01, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80, 0x100, 0x200,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0};
main(int argc, char **argv) {
int i;
int *ret = tetrisProfile(stack);
for(i = 0; i < WIDTH; i++)
printf("ret[%02d]=%d\n", i, ret[i]);
free(ret);
}
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