Sorting algorithm (bubble sort, direct sort, reverse sort)

One, bubble sort

Similar to the upsurge of bubbles, the data will continue to move forward in the array from small to large or from large to small

1.1 Basic idea

The basic idea of ​​bubble sorting is to compare the values ​​of two adjacent elements, exchange the element values ​​if the conditions are met, move the smaller element to the front of the array, and move the larger element to the back of the array (that is, the exchange of two elements Position) so that the smaller element rises from the bottom to the top like a bubble.

1.2 Algorithm ideas

The bubbling algorithm is implemented by a double-layer loop, where the outer loop is used to control the number of sorting rounds, generally the length of the array to be sorted minus 1 time, because there is only one array element left in the last loop, no comparison is needed, and the array has been sorted Up. The inner loop is mainly used to compare the size of each adjacent element in the array to determine whether to exchange positions. The number of comparisons and exchanges decreases with the number of sorting rounds.

1.3 Example

arr=(54 3 1233 -4 135 31 1)
echo "原数组为：${arr[*]}"
length=${#arr[*]}
for  ((a=1;a<$length;a++))
 do
  for  ((b=0;b<$length-a;b++))
   do  
    if [ ${arr[$b]} -gt ${arr[$[$b+1]]} ]
    then
      temp=${arr[$b]}
      arr[$b]=${arr[$[$b+1]]}
      arr[$[$b+1]]=$temp
    fi  
   done
 done
echo "新数组为：${arr[*]}"

Second, select and sort directly

Compared with bubble sort, direct selection sort has fewer exchanges, so it is faster

2.1 Basic idea

Compare the specified sort position with other array elements. If the condition is met, the element value will be exchanged. Note that the difference is bubble sorting. Instead of exchanging adjacent elements, the element that meets the condition is exchanged with the specified sort position (such as from the last The elements begin to be sorted), so that the sorted position gradually expands, and finally the entire array becomes the sorted format.

2.2 Example

arr=(25 31 2 45 123 312 4)
echo "原数组为：${arr[*]}"
length=${#arr[*]}
for ((a=1;a<$length;a++))
 do
  index=0
   for  ((b=1;b<=$length-a;b++))
    do  
     if [ ${arr[$b]} -gt ${arr[$index]} ];then
        index=$b
     fi  
    done
    temp=${arr[$length-$a]}
    arr[$length-$a]=${arr[$index]}
    arr[$index]=$temp
done
echo "新数组为：${arr[*]}"

Three, reverse sort

Reorder the contents of the original array in reverse order

3.1 Basic idea

Replace the last element of the array with the first element. The penultimate element is replaced with the second element, and so on, until all the array elements are reversed and replaced

3.2 Example

arr=(10 20 30 40 50 60) 
echo "原数组为：${arr[*]}"

length=${#arr[*]}
 for ((a=0; a<$length/2; a++))
  do  
   temp=${arr[$a]}
   arr[$a]=${arr[$lenqth-$a-1]}
   arr[$length-$a-1]=$temp
  done
echo "新数组为：${arr[*]}"