简单查找算法小结:

简单查找算法小结:

前两种是线性查找及及其改进版,都比较的简单,在这里就不多做介绍了,算法的最低效率为O(n).

long linearSearch(Type* arr,long len,Type target)

{

       long i=0,ansPos;

       ansPos=-1;

       for(i=0;i<len;i++)

              if(arr[i]==target)

              {

                     ansPos=i;

                     break;

              }

       return ansPos;

}

 

//a linear search with a sorted list

long linearSearch2(Type* arr,long len,Type target)

{

       long i,ansPos;

      

       ansPos=-1;

      

       for(i=0;i<len;i++)

              if(arr[i]>=target)

              {

                     ansPos=i;

                     break;

              }

       if(arr[i]>target)

       {

              ansPos=-1;

              printf("/n data not found./n");

       }

      

       return ansPos;

}

 

 

二分查找法,是Conquer and Divide思想的简单而又生动的一个实现,它在最慢情况下的运行效率为O(logn) ,(log 表示以2为底的对数函数)

参

http://blog.youkuaiyun.com/emilmatthew/archive/2005/08/07/447725.aspx

 

long bSearch(Type* arr,long len,Type target)

{

       long l,u,m,ansPos;

       assertF(arr!=NULL,"in bSearch,arr is NULL/n");

      

       l=0;u=len-1;ansPos=-1;

       while(l<=u)

       {

              m=(l+u)/2;

              if(target<arr[m])

                     u=m-1;

              else if(target==arr[m])

              {    

                     ansPos=m;

                     break;

              }

              else

              {

                     l=m+1;

              }

       }

       if(ansPos==-1) printf("/nIn bsearch,data not founc/n");

             

       return ansPos;

}

 

测试:

       当数据量达到10,000,000时,线性查找及改进的线性查找算法的平均消耗时间单位在0.01秒的级别,而二分查找的平均消耗时间仍为0.0000s,也就是万分之一秒这个等级下.