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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. 	//この関数の内側だけを書く
  8. 	int r, s, t;
  9. 	for(r = 0, s = n - 1; r <= s; ){
  10. 		t = (r + s) / 2;
  11. 		if(a[t] == x){
  12. 			return t;
  13. 		}
  14. 		else if(a[t] < x){
  15. 			r = t + 1;
  16. 		}
  17. 		else
  18. 			s = t - 1;
  19. 	}
  20.  
  21. 	return -1;
  22. }
  23.  
  24.  
  25. int main(void) {
  26. 	int n,x,i;
  27. 	int *a;
  28. 	int ans = -1;
  29. 	scanf("%d %d",&n,&x);
  30. 	a = (int*)malloc(sizeof(int)*n);
  31. 	if(a==NULL){
  32. 		printf("ERROR\n");
  33. 		return -1;
  34. 	}
  35. 	for(i=0;i<n;i++){
  36. 		scanf("%d",&a[i]);
  37. 	}
  38. 	ans = binary_search(a,n,x);
  39. 	if(ans != -1) printf("a[%d] = %d\n",ans,a[ans]);
  40. 	else printf("not found\n");
  41. 	free(a);
  42. 	return 0;
  43. }
  44.  
Success #stdin #stdout 0s 5292KB
comments (?)
stdin 
12 5
1 2 3 4 5 8 9 13 16 21 25 27
stdout 
a[4] = 5
https://ideone.com/RElrlz
language:
C (gcc 8.3)
created:
3 days ago
visibility:
public

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