查找之折半查找

折半查找的前提是有序的，与中间值进行比较，如果有序的则返回；否则，改变始末位置，再进行查找

实现方法：1 循环实现  2 递归实现

1 循环实现
#include<stdio.h>
int binary_search(int *array,int n,int data);
int main()
{
 int array[10]={
 1,2,3,4,5,6,7,8,9,10
 }; 
 printf("please input the number that you want search\n");
 int num;
 scanf("%d",&num);
 int result=binary_search(array,10,num);
 if(result==-1)
 {
  printf("not found %d\n",num);
 }
 else
  printf("the index is %d\n",result);
} 
int binary_search(int *array,int n,int data)
{
 int start,end,mid;
 start=0;
 end=n-1;
 while(start<=end)
 {
  mid=(start+end)/2;
  if(array[mid]==data)
  {
   return mid;
  }
  else if(array[mid]>data)
  {
   end=mid-1;
  }
  else
  {
   start=mid+1;
  }
 }
 return -1;   
}

2 递归实现

int binary_search2(int *array,int start,int end ,int value)
{ if(start>end) return -1;
 int mid=(start+end)/2;
 if(array[mid]==value)
 {
  return mid;
 } 
 else if(array[mid]>value)
 {
  binary_search2(array,start,mid-1,value); 
 }
 else
  binary_search2(array,mid+1,end,value);
}