Data-structures-algorithms-binary-search-program-in-c

Cのバイナリ検索プログラム

バイナリ検索は、実行時の複雑さがΟ（log n）の高速検索アルゴリズムです。 この検索アルゴリズムは、分割統治の原則に基づいて機能します。 このアルゴリズムが適切に機能するためには、データ収集がソートされた形式である必要があります。

Cでの実装

#include <stdio.h>

#define MAX 20

//array of items on which linear search will be conducted.
int intArray[MAX] = {1,2,3,4,6,7,9,11,12,14,15,16,17,19,33,34,43,45,55,66};

void printline(int count) {
   int i;

   for(i = 0;i <count-1;i++) {
      printf("=");
   }

   printf("=\n");
}

int find(int data) {
   int lowerBound = 0;
   int upperBound = MAX -1;
   int midPoint = -1;
   int comparisons = 0;
   int index = -1;

   while(lowerBound <= upperBound) {
      printf("Comparison %d\n" , (comparisons +1) );
      printf("lowerBound : %d, intArray[%d] = %d\n",lowerBound,lowerBound,
         intArray[lowerBound]);
      printf("upperBound : %d, intArray[%d] = %d\n",upperBound,upperBound,
         intArray[upperBound]);
      comparisons&plus;&plus;;

     //compute the mid point
     //midPoint = (lowerBound &plus; upperBound)/2;
      midPoint = lowerBound &plus; (upperBound - lowerBound)/2;

     //data found
      if(intArray[midPoint] == data) {
         index = midPoint;
         break;
      } else {
        //if data is larger
         if(intArray[midPoint] < data) {
           //data is in upper half
            lowerBound = midPoint &plus; 1;
         }
        //data is smaller
         else {
           //data is in lower half
            upperBound = midPoint -1;
         }
      }
   }
   printf("Total comparisons made: %d" , comparisons);
   return index;
}

void display() {
   int i;
   printf("[");

  //navigate through all items
   for(i = 0;i<MAX;i&plus;&plus;) {
      printf("%d ",intArray[i]);
   }

   printf("]\n");
}

void main() {
   printf("Input Array: ");
   display();
   printline(50);

  //find location of 1
   int location = find(55);

  //if element was found
   if(location != -1)
      printf("\nElement found at location: %d" ,(location+1));
   else
      printf("\nElement not found.");
}

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上記のプログラムをコンパイルして実行すると、次の結果が生成されます-

出力

Input Array: [1 2 3 4 6 7 9 11 12 14 15 16 17 19 33 34 43 45 55 66 ]
==================================================
Comparison 1
lowerBound : 0, intArray[0] = 1
upperBound : 19, intArray[19] = 66
Comparison 2
lowerBound : 10, intArray[10] = 15
upperBound : 19, intArray[19] = 66
Comparison 3
lowerBound : 15, intArray[15] = 34
upperBound : 19, intArray[19] = 66
Comparison 4
lowerBound : 18, intArray[18] = 55
upperBound : 19, intArray[19] = 66
Total comparisons made: 4
Element found at location: 19

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