• C언어 문법은 일단 여기까지
  
• 본격적 알고리즘 시작
  
• 선형 자료 구조(linear data structure)
  
  • 배열(array) : fixed-sized collection of contiguous data
    
    • random access
      
  • 연결 리스트(linked list) : sequential of data linked by pointer
    
    • node - link
      
  • array v.s. linked list
    
• algorithms for sequential data
  
  • 탐색(search)
    
    • 선형 탐색(linear search)
      
    • 이진 탐색(binary search)
      
  • 정렬(sort)
    
    • 선택 정렬(selection sort)
      
    • 삽입 정렬(insertion sort)
      
    • 병합 정렬(merge sort)
      
      • divide-and-conqurer
        
    • 퀵 정렬(quick sort)
      
    • performance
      
      • big-O notation(big-Omega, big-Theta)
        
      • speed, time complexity
        
      • memory, space complexity, in-place sort
        
      • stablity
        
    • swap sort v.s. others
      
      • e.g) counting sort, radix sort
        
  • 이번주는 일정이 안맞아 휴강; 다음주에 이 내용으로 진행합니다.
    

• selection_sort, insertion_sort, merge_sort, quick_sort(,bubble_sort : optional)
  
• <sort_instruction> input_file [output_file]
  
• any language
  
• input :
  
  • 1st line : # of line N
    
  • 2nd ~ : (unsorted) N integers
    
• output:
  
  • N line : sorted N integers
    
  • N + 1 line : elapsed time (in millisecond)
    
  • print in output file; if no argument, to standard output(terminal console)
    
    

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<time.h>

#define swap(type,x,y) type t = x; x = y; y = t; //교환함수

void selection(void); //선택정렬
void insertion(void); //삽입정렬
void merge(int,int); //병합정렬
void quick(int,int); //퀵정렬
void bubble(void); //버블정렬
void output(char*); //(output.txt로 정렬된 수열과 elapsed time 출력) or 표준출력

int n;
int *a;
int *buff;

double milsec;
time_t start, end;

FILE *input_file;
FILE *output_file;

int main(int argc, char* argv[]){
  int i;
  char num[10]; //n은 1,000,000,000미만.

  input_file = fopen(argv[2],"r");
  output_file = fopen(argv[3],"w");

  if(input_file == NULL){;
    printf("ERROR_InputFile\n");
    return 0;
  }//input_file이 존재하지 않으면 에러 출력.

  fgets(num,sizeof(num),input_file);
  n = atoi(num); //배열의 크기 N을 구함.
  a = calloc(n,sizeof(int));

  for(i=0;i<n;i++){
    fscanf(input_file,"%d",&a[i]); //배열 a에 정렬되지 않은 수 받기.
  }

  //명령받기.
  if(!strcmp(argv[1],"selection")) selection();
  else if(!strcmp(argv[1],"insertion")) insertion();
  else if(!strcmp(argv[1],"merge")){
    buff = calloc(n,sizeof(int));
    merge(0,n-1);
    free(buff);
  }
  else if(!strcmp(argv[1],"quick")) quick(0,n-1);
  else if(!strcmp(argv[1],"bubble")) bubble();
  else printf("Wrong_SortInstruction");

  //결과출력.
  output(argv[3]);

  //배열해제 및 파일닫기.
  free(a);
  fclose(input_file);
  fclose(output_file);

  return 0;
}

//선택정렬
void selection(void){
  start = clock();
  int i, j;
  for(i=0;i<n-1;i++){
    int min = i;
    for(j=i+1;j<n;j++){
      if(a[j]<a[min]){
        min = j;
      }
    }
    swap(int,a[i],a[min]);
  }
  end = clock();
}

//삽입정렬
void insertion(void){
  start = clock();
  int i,j;
  for(i=1;i<n;i++){
    int tmp = a[i];
    for(j=i; j>0 && a[j-1]>tmp; j--){
      a[j] = a[j-1];
    }
    a[j] = tmp;
  }
  end = clock();
}

//병합정렬
void merge(int left, int right){
  start = clock();
  if(left<right){
    int i, j = 0, k = left, p = 0;
    int center = (left + right) / 2;
    merge(left,center);
    merge(center+1,right);
    for(i=left;i<=center;i++){
      buff[p++] = a[i];
    }
    while(i<=right && j<p){
      a[k++] = (buff[j]<=a[i]) ? buff[j++] : a[i++];
    }
    while(j<p){
      a[k++] = buff[j++];
    }
  }
  end = clock();
}

//퀵정렬
void quick(int left, int right){ //재귀적인 방식.
  start = clock();
  int pl = left;
  int pr = right;
  int x = a[(pl+pr)/2];
  do{
    while(a[pl] < x) pl++;
    while(a[pr] > x) pr--;
    if(pl <= pr){
      swap(int,a[pl],a[pr]);
      pl++;
      pr--;
    }
  }while(pl <= pr);
  if(left < pr) quick(left,pr);
  if(pl < right) quick(pl,right);
  end = clock();
}//비재귀적인 방법은 스택을 활용.

//버블정렬
void bubble(void){
  start = clock();
  int i = 0, j;
  while(i<n-1){
    int last = n-1; //가장 마지막으로 교환이 일어난 위치
    for(j=n-1;j>i;j--){
      if(a[j]<a[j-1]){
        swap(int,a[j],a[j-1]);
        last = j;
      }
    }
    i = last;
  }
  end = clock();
}

//출력함수
void output(char* argv){
  int i;
  milsec = 1000.0 * (end-start) / CLOCKS_PER_SEC;
  if(argv){
    for(i=0;i<n;i++){
      fprintf(output_file,"%d ",a[i]); //정렬된 배열 a 출력
    }
    fprintf(output_file,"\n");
    fprintf(output_file,"elapsed_time = %.3f ms\n",milsec); //elapsed_time 출력
  }
  else{
    for(i=0;i<n;i++){
      printf("%d ",a[i]);
    }
    printf("\n");
    printf("elapsed_time = %.3f ms\n",milsec);
  }
}
//힘들어ㅠㅠ