在PHP中,是否可以轻松地“旋转”数组?
就像这样: 1、2、3、4 -> 2、3、4、1
是否有某种内置的PHP函数可以实现这个功能?
$numbers = array(1,2,3,4);
array_push($numbers, array_shift($numbers));
print_r($numbers);
输出
Array
(
[0] => 2
[1] => 3
[2] => 4
[3] => 1
)
array_unshift($numbers,array_pop($numbers));
- Titus大多数当前的答案是正确的,但仅适用于您不关心索引的情况:
$arr = array('foo' => 'bar', 'baz' => 'qux', 'wibble' => 'wobble');
array_push($arr, array_shift($arr));
print_r($arr);
输出:
Array
(
[baz] => qux
[wibble] => wobble
[0] => bar
)
为保留你的索引,你可以像这样做: To preserve your indices you can do something like:
$arr = array('foo' => 'bar', 'baz' => 'qux', 'wibble' => 'wobble');
$keys = array_keys($arr);
$val = $arr[$keys[0]];
unset($arr[$keys[0]]);
$arr[$keys[0]] = $val;
print_r($arr);
输出:
Array
(
[baz] => qux
[wibble] => wobble
[foo] => bar
)
或许有人能比我更简洁地完成旋转,但这个方法仍然有效。
list($k,$v)=each($arr);unset($arr[$k]);$arr[$k]=$v;
。你可能需要在前面加上 reset($arr);
。 - Titus这非常简单,可以用多种方法来实现。例如:
$array = array( 'a', 'b', 'c' );
$array[] = array_shift( $array );
shift
和push
可能是旋转数组的常见方式,但往往会破坏您的键。更加健壮的方法是使用array_merge
和array_splice
的组合。/**
* Rotates an array.
*
* Numerical indexes will be renumbered automatically.
* Associations will be kept for keys which are strings.
*
* Rotations will always occur similar to shift and push,
* where the number of items denoted by the distance are
* removed from the start of the array and are appended.
*
* Negative distances work in reverse, and are similar to
* pop and unshift instead.
*
* Distance magnitudes greater than the length of the array
* can be interpreted as rotating an array more than a full
* rotation. This will be reduced to calculate the remaining
* rotation after all full rotations.
*
* @param array $array The original array to rotate.
* Passing a reference may cause the original array to be truncated.
* @param int $distance The number of elements to move to the end.
* Distance is automatically interpreted as an integer.
* @return array The modified array.
*/
function array_rotate($array, $distance = 1) {
settype($array, 'array');
$distance %= count($array);
return array_merge(
array_splice($array, $distance), // Last elements - moved to the start
$array // First elements - appended to the end
);
}
// Example rotating an array 180°.
$rotated_180 = array_rotate($array, count($array) / 2);
另外,如果您也需要旋转密钥以匹配不同的值,您可以结合使用 array_keys
、array_combine
、array_rotate
和 array_values
。
/**
* Rotates the keys of an array while keeping values in the same order.
*
* @see array_rotate(); for function arguments and output.
*/
function array_rotate_key($array, $distance = 1) {
$keys = array_keys((array)$array);
return array_combine(
array_rotate($keys, $distance), // Rotated keys
array_values((array)$array) // Values
);
}
或者,可以在保持键的顺序不变的同时旋转值(相当于调用匹配的array_rotate_key
函数调用中的负距离)。
/**
* Rotates the values of an array while keeping keys in the same order.
*
* @see array_rotate(); for function arguments and output.
*/
function array_rotate_value($array, $distance = 1) {
$values = array_values((array)$array);
return array_combine(
array_keys((array)$array), // Keys
array_rotate($values, $distance) // Rotated values
);
}
/**
* Rotates an array while keeping all key and value association.
*
* @see array_rotate(); for function arguments and output.
*/
function array_rotate_assoc($array, $distance = 1) {
$keys = array_keys((array)$array);
$values = array_values((array)$array);
return array_combine(
array_rotate($keys, $distance), // Rotated keys
array_rotate($values, $distance) // Rotated values
);
}
进行一些基准测试可能会有益,但我认为每个请求只旋转少量数据,无论使用哪种方法,都不会明显影响性能。
也可以使用自定义排序函数来旋转数组,但这很可能过于复杂。例如usort
。
一种维护键和旋转的方法。使用与array_push(array,array_shift(array))相同的概念,而是使用2个array_slice的array_merge。
$x = array("a" => 1, "b" => 2, "c" => 3, 'd' => 4);
将第一个元素移动到末尾
array_merge(array_slice($x,1,NULL,true),array_slice($x,0,1,true))
//'b'=>2,'c'=>3,'d'=>4,'a'=>1
将最后一个元素移动到前面
array_merge(array_slice($x,count($x)-1,1,true) ,array_slice($x,0,
//'d'=>4,'a'=>1,'b'=>2,'c'=>3
array_push
和array_shift
将适用于除最后一个测试用例以外的所有测试用例,由于超时而失败。因此,array_push
和array_shift
不会给您最快的解决方案。function leftRotation(array $array, $n) {
for ($i = 0; $i < $n; $i++) {
$value = array[$i]; unset(array[$i]); array[] = $value;
}
return array;
}
function arr_rotate(&$array,$rotate_count) {
for ($i = 0; $i < $rotate_count; $i++) {
array_push($array, array_shift($array));
}
}
用法:
$xarr = array('1','2','3','4','5');
arr_rotate($xarr, 2);
print_r($xarr);
结果:
Array ( [0] => 3 [1] => 4 [2] => 5 [3] => 1 [4] => 2 )
arr_rotate($xarr, count($xarr));
可以得到相同的结果顺序。添加 $rotate_count %= count($array);
这一行代码将确保最大迭代次数始终小于元素数量。 - Shaun Cockerill$daynamesArray = array("Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday");
array_push($daynamesArray, array_shift($daynamesArray)); //shift by one
array_push($daynamesArray, array_shift($daynamesArray)); //shift by two
print_r($daynamesArray);
输出从“Wednesday”开始:
Array ( [0] => Wednesday [1] => Thursday [2] => Friday [3] => Saturday [4] => Sunday [5] => Monday [6] => Tuesday
是的,这里有一个我自己写的函数,其中$A是数组,$K是您想要旋转数组的次数:
function solution($A, $K) {
for($i = 0; $i < $K; $i++): //we cycle $K
$arrayTemp = $A;
for($j = 0; $j < count($arrayTemp); $j++): // we cycle the array
if($j == count($arrayTemp) - 1) $A[0] = $arrayTemp[$j]; // we check for the last position
else $A[$j + 1] = $arrayTemp[$j]; // all but last position
endfor;
endfor;
return $A;
}