Sharing three methods of sorting arrays in PHP_PHP Tutorial-PHP Tutorial-php.cn

Sharing three methods of sorting arrays in PHP_PHP Tutorial

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Release： 2016-07-21 15:18:27

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1. Bubble sorting method
Instructions: Find the largest number, arrange it to the end, and then continue to find

Example:

Copy the code The code is as follows:

 
$arr = array(3,5,-1,0,2); 
for($i=0;$i< count($arr)-1;$i++){ 
for($j=0;$jif($arr[$j ]>$arr[$j+1]){ 
$temp = $arr[$j]; 
$arr[$j]=$arr[$j+1]; 
$arr [$j+1]=$temp; 
} 
} 
} 

Understanding:
3, 5, -1, 0, 2
/ /Start from the first number and compare backwards. If it is larger than the following number, adjust the position with the following number
//The first time, 3 is less than 5, then it remains unchanged
//The second time, 5 is greater than -1, then it becomes
3, -1, 5, 0, 2
//The third time, 5 is greater than 0
3, -1, 0, 5, 2
// The fourth time, 5 is greater than 2
3, -1, 0, 2, 5
This completes an inner loop. At this time, the last number is sorted and will not participate next time.
3, -1, 0, 2, 5 The second outer loop starts. The first time: 3 is greater than -1
-1, 3, 0, 2, 5
The second time: 3 is greater than 0
-1, 0, 3, 2, 5
The third time: 3 is greater than 2
-1, 0, 2, 3, 5
This completes the sorting of the next two digits, and then analogizes
-1, 0, 2, 3, 5
2. Selection sorting method
Description: First assume that the first number is the smallest number, and then compare the following numbers with it in sequence. If the assumed If the number is not the smallest number, swap it with the following smallest number

Copy the code The code is as follows:

 
$ arr=array(2,1,-1,3,0); 
for($i=0;$i$minval = $arr[ $i]; 
$minindex = $i; 
for($j=1+$i;$jif($arr[$j] <$minval){ 
$minval = $arr[$j]; 
$minindex = $j; 
} 
} 
$temp = $arr[$i]; 
$arr[$i] = $arr[$minindex]; 
$arr[$minindex] = $temp; 
} 

Understanding:
2, 1 , -1, 3, 0
//Assume that the first number 2 is the minimum value, and the subsequent numbers are compared with 2 in turn to find the smallest number
Process:
1 is less than 2 , then minval=1
-1 is less than 1, then minval=-1
3 is greater than -1, unchanged
0 is greater than -1, unchanged
Then now find the smallest value in the array The number is -1
Swap the positions of -1 and 2 to complete the sorting of the first number
Then the array now becomes
-1, 1, 2, 3, 0
Now The first number -1 is already in order, so it does not participate in the comparison. Continue
Now assume that minval=1
2 is greater than 1, unchanged
3 is greater than 1, unchanged
0 Less than 1, then minval=0
Now one loop is completed, swap the positions of 0 and 1 to complete the sorting of the second number
Then now the array becomes
-1, 0, 2, 3, 1
//The following push method is the same as above. . .

3. Insertion sort method

Explanation: First assume that the first number in an array is a separate ordered array, and then combine the next number with it [As I grows here, it becomes them] Compare, if the following number is smaller than the assumed number, move the smaller number back, and finally move that number to the front

Copy code The code is as follows:

 
$arr=array(2,1,-1,3,0); 
for($ i=1;$i$insertval=$arr[$i]; 
$insertindex = $i-1; 
while($insertindex>= 0 && $insertval<$arr[$insertindex]){ 
$arr[$insertindex+1]=$arr[$insertindex]; 
$insertindex--; 
} 
$temp = $arr[$i]; 
$arr[$insertindex+1]=$insertval; 
} 

Understanding:
2, 1, -1, 3, 0
//For the first time, save the number 1 to be inserted as insertval, and then compare insertval with 2. 1 is less than 2, so put 2 is moved back and becomes the following picture
2, 2, -1, 3, 0
//At this time, there is no number in front of 2, insertindex=0, so the comparison is completed, then insert insertval to find of this location. It becomes as shown below
1, 2, -1, 3, 0
//At this time, 1, 2 becomes an ordered array
//The second time, first save the number to be inserted -1 is insertval, and then compare insertval with 2. -1 is less than 2, so move 2 back and become the following picture
1, 2, 2, 3, 0
//At this time, compare insertval with 2. 1 is compared, -1 is less than 1, then -1 is moved back and becomes the following picture (this is a process of comparing the number to be inserted with the previous ordered array)
1, 1, 2, 3, 0
//At this point, insertindex has come to an end, so insert insertval at this position
-1, 1, 2, 3, 0
//The following method is as above