Bubble Sort Algorithm

                                               Bubble Sort   

Topic description

Find and sort

Question: Enter any (user, grade) sequence, and you can get grades from high to low or from low to high. The same grades
      are processed according to the rule of entering first and ranking first.

   Example:
   jack 70
   peter 96
   Tom 70
   smith 67

   High to Low Grade            
   peter 96    
   jack 70    
   Tom 70    
   smith 67    

   low to high

   smith     67  

   jack       70    
   Tom      70    
   peter     96      

Enter description:

Enter multiple lines, first enter the number of people to be sorted, then enter the sorting method 0 (descending order) or 1 (ascending order), then enter their names and grades respectively, separated by a space

Output description:

Output name and grade as specified, separated by a space

Example 1

enter

3
0
fang 90
the 50
and 70

output

fang 90
and 70
the 50

#include<stdio.h>
#include<string.h>
struct node{
  char name[20];
  int score;
};
int flag;
struct node *BubleSort(struct node student[],int n){
  char name[20];
  for(int i=0;i<n;i++){
     for (int j=0;j<n-i-1;j++){
       if(student[j].score>student[j+1].score&&flag==1){     //升序
         int score=student[j+1].score;
         strcpy(name,student[j+1].name);
         student[j+1].score=student[j].score;
         strcpy(student[j+1].name,student[j].name);
         student[j].score=score;
         strcpy(student[j].name,name);
       }
       else if(student[j].score<student[j+1].score&&flag==0){  //降序
       	 int score=student[j+1].score;
         strcpy(name,student[j+1].name);
         student[j+1].score=student[j].score;
         strcpy(student[j+1].name,student[j].name);
         student[j].score=score;
         strcpy(student[j].name,name);
	   }
     }
  }
    return student;
}
int main(){
  struct node student[100];
  struct node *result;
  int n;
  while(scanf("%d%d",&n,&flag)!=EOF){
  for(int i=0;i<n;i++){
    scanf("%s%d",student[i].name,&student[i].score);
  }
  result=BubleSort(student,n);
  for(int i=0;i<n;i++){
    printf("%s %d\n",result[i].name,result[i].score);
     }
  }
  return 0;
}

time complexity

       If the initial state of the file is in positive order, the sorting can be completed in one scan.  Minimum  required number of keyword comparisons and number  of record moves  :  ,  . Therefore, the best time complexity of bubble sort is  .

       If the original file is in reverse order, a   pass sorting is required. Each time sorting needs to perform   sub-key comparison (1≤i≤n-1), and each comparison must move the record three times to exchange the record position. In this case, both comparisons and moves are at their maximum:

                                           

The worst time complexity of bubble sort is   . To sum up, so the total average time complexity of bubble sort is  

Algorithm Stability

        Bubble sort is to move small elements forward or large elements backward. The comparison is two adjacent elements. When the two elements are equal, the position of the element will not change, so the bubbling algorithm is a stable algorithm.