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  1. //第３回提出課題
  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. //この関数の内側だけを書く
  8. int mid, lef, rig;
  9. lef = 0;
  10. rig = n - 1;
  11. while (1) {
  12. mid = (lef + rig) / 2;
  13.   if (a[mid] == x) {
  14.     return mid;
  15.   } else if (x < a[mid]) {
  16.       rig = mid - 1;
  17.       if (a[rig] == x) {
  18.         return rig;
  19.       }
  20.     } else {
  21.         lef = mid + 1;
  22.         if (a[lef] == x) {
  23.           return lef;
  24.         }
  25.       }
  26.   if (lef >= rig) {
  27.     return -1;
  28.   }
  29. }
  30. return -1;
  31. }
  32.  
  33. int main(void) {
  34. 	int n,x,i;
  35. 	int *a;
  36. 	int ans = -1;
  37. 	scanf("%d %d",&n,&x);
  38. 	a = (int*)malloc(sizeof(int)*n);
  39. 	if(a==NULL){
  40. 		printf("ERROR\n");
  41. 		return -1;
  42. 	}
  43. 	for(i=0;i<n;i++){
  44. 		scanf("%d",&a[i]);
  45. 	}
  46. 	ans = binary_search(a,n,x);
  47. 	if(ans != -1) printf("a[%d] = %d\n",ans,a[ans]);
  48. 	else printf("not found\n");
  49. 	free(a);
  50. 	return 0;
  51. }
Success #stdin #stdout 0.01s 5464KB
comments (?)
stdin
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12 5 1 2 3 4 5 8 9 13 16 21 25 27
stdout
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a[4] = 5
https://ideone.com/0VDjKp
language:
C (gcc 8.3)
created:
1 year ago
visibility:
public

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