Algs4-1.1.29等值键

1.1.29等值键。为BinarySearch类添加一个静态方法rank(),它接受一个键和一个整型有序数组（可能存在重复键）作为参数并返回数组中小于该键的元素数量，以及一个类似的方法count()来返回数组中等于该键的元素的数量。注意：如果i和j分别是rank(key,a)和count(key,a)的返回值，那么a[i...i+j-1]就是数组中所有和key相等的元素。
import java.util.Arrays;
public class BinarySearch
{
public static void main(String[] args)
    {
        int[] whitelist=In.readInts(args[0]);
        Arrays.sort(whitelist);
        while (!StdIn.isEmpty())
        {
            int key=StdIn.readInt();
            StdOut.printf("small "+ Integer.toString(key) + " num=%d ,count=%d",rank(key,whitelist),count(key,whitelist));
        }  
    }//end main

    public static int rank(int key,int[] a)
    {
        int smallCount=findSmallKeyIndex(key,a);
        if (smallCount<1) return 0;
        else return smallCount;
    }//end rank
   
    public static int count(int key,int[] a)
    {
        int smallKeyIndex=findSmallKeyIndex(key,a);
        int bigKeyIndex=findBigKeyIndex(key,a);
        if (smallKeyIndex==-1) return 0;
        else  return bigKeyIndex-smallKeyIndex+1;
    }//end count
   
    public static int findSmallKeyIndex(int key,int[] a)
    {
        int indexOfKey=findKeyIndex(key,a);
        //key‘s index is 0 or -1 then no one is  small   than the key.
        if (indexOfKey==-1 )
            return -1;
        else if(indexOfKey==0)
            return 0;
        else //(indexOfKey>0)
        {
            indexOfKey--; 
            //find to 0
           while (indexOfKey>=0 && a[indexOfKey]==key)    indexOfKey--;
           if (indexOfKey>0)  return indexOfKey+1;
           else if(indexOfKey==0 && a[indexOfKey]<key) return indexOfKey+1;
           else//(indexOfKey==0 && a[indexOfKey]==key)
           return 0;
        } 
   }//end findSmallKeyIndex
   
    public static int findBigKeyIndex(int key,int[] a)
    {
        int indexOfKey=findKeyIndex(key,a);
        //not found or found the last then no one is big than the key.
        if (indexOfKey==-1)
            return -1;
        else if(indexOfKey==a.length-1)
            return indexOfKey;
        //find to end
        else //(indexOfKey>=0 && indexOfKey<a.length-1)
        {
            indexOfKey++;
            while(indexOfKey<a.length && a[indexOfKey]==key) indexOfKey++;
            if(indexOfKey<a.length-1) return indexOfKey-1;
            else if(indexOfKey==a.length-1 && a[indexOfKey]>key) return indexOfKey-1;
            else//(indexOfKey==a.length-1 && a[indexOfKey]==key)
            return a.length-1;
          }
    }//findBigKeyIndex
   
    public static int findKeyIndex(int key,int[]a)
    {
        int lo=0;
        int hi=a.length-1;
        while (lo<=hi)
        {
            int mid=lo+(hi-lo)/2;
            if (key<a[mid]) hi=mid-1;
            else if(key>a[mid]) lo=mid+1;
            else return mid;
          }
        return -1;
     }//findKey

  
}