【剑指offer】数字在排序数组中出现的次数

2013-09-02 16:28:35

找出数字在排序数组中出现的次数。

注意几点：

1. 一开始试图用size_t类型表示数组的下标begin、end，到那时这样做在end = 0时，end - 1是size_t类型的最大值，仍然满足begin <= end，但此时将会对sortedArray数组中下标为size_t类型的最大值的元素，会出现访问越界；因此，对于数组小标，不要为了保证是整数二用size_t类型，用int类型比较好。
2. 若用int型表示，就不需要用STATUS的状态标志，下面的程序中没有修改这一点。

代码：

 #include <iostream>
 #include <cassert>
 using namespace std;

 typedef int DataType;

 const bool SuccessToFind = true;
 const bool FailToFind = false;

 bool STATUS = SuccessToFind;

 //找出第一个K出现的位置的下标
 int GetFirstK(DataType *sortedArray,int begin,int end,const DataType data)
 {
     /*assert(NULL != sortedArray);
     assert(begin <= end);*/

     STATUS = FailToFind;
     int mid = ;

     while (begin <= end)
     {
         mid = begin + (end - begin) / ;
         if (sortedArray[mid] == data)
         {
             if (mid == begin || sortedArray[mid - ] != data)
             {
                 STATUS = SuccessToFind;
                 return mid;
             }
             else
             {
                 end = mid - ;
             }
         }
         else if (sortedArray[mid] < data)
         {
             begin = mid + ;
         }
         else
         {
             end = mid - ;   //mid为0时，若end为size_t类型，会出错
         }
     }

     STATUS = FailToFind;
     return ;
 }

 //找出最后一个K出现的位置的下标
 int GetLastK(DataType *sortedArray,int begin,int end,const DataType data)
 {
     /*assert(NULL != sortedArray);
     assert(begin <= end);*/

     STATUS = FailToFind;
     int mid = ;

     while (begin <= end)
     {
         mid = begin + (end - begin) / ;
         if (sortedArray[mid] == data)
         {
             if (mid == end || sortedArray[mid + ] != data)
             {
                 STATUS = SuccessToFind;
                 return mid;
             }
             else
             {
                 begin = mid + ;
             }
         }
         else if (sortedArray[mid] < data)
         {
             begin = mid + ;
         }
         else
         {
             end = mid - ;
         }
     }

     STATUS = FailToFind;
     return ;
 }

 //返回K出现的次数
 int GetNumberOfK(DataType *sortedArray,int len,const DataType data)
 {
     assert(NULL != sortedArray);
     assert(len >= );

     size_t begin = GetFirstK(sortedArray,,len - ,data);
     size_t end = GetLastK(sortedArray,,len - ,data);

     if (STATUS == SuccessToFind)
     {
         return (end - begin + );
     }
     else
     {
         return ;
     }
 }

 //测试GetNumberOfK
 void TestGetNumberOfK()
 {
     DataType sortedArray[] = {,,,, ,,,, ,};
     size_t len = ;
     DataType data = ;

     cout<<"please enter the data to find ,end with ctrl+z "<<endl;
     while (cin>>data)
     {
         cout<<"the number of "<<data<<" in array is : "<<GetNumberOfK(sortedArray,len,data)<<endl;
         cout<<"please enter the data to find ,end with ctrl+z "<<endl;
     }

 }

 int main()
 {
     TestGetNumberOfK();
     return ;
 }

测试结果：

please enter the data to find ,end with ctrl+z

the number of  in array is :
please enter the data to find ,end with ctrl+z

the number of  in array is :
please enter the data to find ,end with ctrl+z

the number of  in array is :
please enter the data to find ,end with ctrl+z

the number of  in array is :
please enter the data to find ,end with ctrl+z
-
the number of - in array is :
please enter the data to find ,end with ctrl+z

the number of  in array is :
please enter the data to find ,end with ctrl+z
^Z
请按任意键继续. . .