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  1. //第3回 課題１
  2. #include <stdio.h>
  3. #include <stdlib.h>
  4.  
  5. //この関数を実装する
  6. int binary_search(int a[],int n,int x){
  7. 	int left=0;
  8. 	int right=n-1;
  9. 	while(left<=right){
  10. 		int c=(left+right)/2;
  11. 		if(a[c]==x){
  12. 			return c;
  13. 		}
  14. 		else if(a[c]<=x){
  15. 			left =c+1;
  16. 		}
  17. 		else if(a[c]>=x){
  18. 			right =c-1;
  19. 		}
  20. 	}
  21. 	return -1;
  22. }
  23.  
  24. int main(void) {
  25. 	int n,x,i;
  26. 	int *a;
  27. 	int ans = -1;
  28. 	scanf("%d %d",&n,&x);
  29. 	a = (int*)malloc(sizeof(int)*n);
  30. 	if(a==NULL){
  31. 		printf("ERROR\n");
  32. 		return -1;
  33. 	}
  34. 	for(i=0;i<n;i++){
  35. 		scanf("%d",&a[i]);
  36. 	}
  37. 	ans = binary_search(a,n,x);
  38. 	if(ans != -1) printf("a[%d] = %d\n",ans,a[ans]);
  39. 	else printf("not found\n");
  40. 	free(a);
  41. 	return 0;
  42. }
  43.  
Success #stdin #stdout 0.01s 5320KB
comments (?)
stdin 
12 5
1 2 3 4 5 8 9 13 16 21 25 27
stdout 
a[4] = 5
https://ideone.com/hGFz7M
language:
C (gcc 8.3)
created:
14 hours ago
visibility:
public

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