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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 lef = 0;
  9.     int rig = n - 1;
  10.     while(lef <= rig){
  11.         int mid = (lef + rig) / 2;
  12.         if(a[mid] == x){
  13.             return mid; // 見つかったらそのインデックスを返す
  14.         } else if(a[mid] < x){
  15.             lef = mid + 1;
  16.         } else if(a[mid]>x) {
  17.             rig = mid - 1;
  18.         }
  19.     }
  20.     return -1; // 見つからなかったら -1 を返す
  21. }
  22.  
  23. int main(void) {
  24. 	int n,x,i;
  25. 	int *a;
  26. 	int ans = -1;
  27. 	scanf("%d %d",&n,&x);
  28. 	a = (int*)malloc(sizeof(int)*n);
  29. 	if(a==NULL){
  30. 		printf("ERROR\n");
  31. 		return -1;
  32. 	}
  33. 	for(i=0;i<n;i++){
  34. 		scanf("%d",&a[i]);
  35. 	}
  36. 	ans = binary_search(a,n,x);
  37. 	if(ans != -1) printf("a[%d] = %d\n",ans,a[ans]);
  38. 	else printf("not found\n");
  39. 	free(a);
  40. 	return 0;
  41. }
  42.  
  43.  
Success #stdin #stdout 0s 5316KB
comments (?)
stdin 
12 5

1 2 3 4 5 8 9 13 16 21 25 27
stdout 
a[4] = 5
https://ideone.com/yJ6DtC
language:
C (gcc 8.3)
created:
3 days ago
visibility:
public

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