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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3.  
  4. //この関数を実装する
  5. int binary_search(int a[],int n,int x){
  6. 	//この関数の内側だけを書く
  7. 	int lef,rig,mid;
  8. 	lef=a[0];
  9. 	rig=a[n-1];
  10. 	mid=(lef+rig)/2;
  11. 	for(int i=0;i<n;i++){
  12. 		if(x>mid){
  13. 			lef=mid+1;
  14. 			mid=(lef+rig)/2;
  15. 		}else if(x<mid){
  16. 			rig=mid-1;
  17. 			mid=(lef+rig)/2;
  18. 		}else if(mid==x){
  19. 			break;
  20. 		}else if(lef>rig){
  21. 			return -1;
  22. 		}
  23. 	}
  24. 	for(int i=0;i<n;i++){
  25. 		if(a[i]==mid){
  26. 			return i;
  27. 		}
  28. 	}
  29. }
  30.  
  31. int main(void) {
  32. 	int n,x,i;
  33. 	int *a;
  34. 	int ans = -1;
  35. 	scanf("%d %d",&n,&x);
  36. 	a = (int*)malloc(sizeof(int)*n);
  37. 	if(a==NULL){
  38. 		printf("ERROR\n");
  39. 		return -1;
  40. 	}
  41. 	for(i=0;i<n;i++){
  42. 		scanf("%d",&a[i]);
  43. 	}
  44. 	ans = binary_search(a,n,x);
  45. 	if(ans != -1) printf("a[%d] = %d\n",ans,a[ans]);
  46. 	else printf("not found\n");
  47. 	free(a);
  48. 	return 0;
  49. }
Success #stdin #stdout 0s 5320KB
comments (?)
stdin
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12 5
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5
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stdout
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a[3] = 5
https://ideone.com/RrypAT
language:
C (gcc 8.3)
created:
4 days ago
visibility:
public

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