二分搜索算法（JAVA Code）

算法是IT从业人员必修的一门学科，好的算法可以让你的程序提高效率！精通算法，是名企的一个敲门砖！

所以从今天开始，我要将算法复习一遍，并且用JAVA代码来实现！

 

二分搜素算法

采用了分而治之的原理，在使用该算法之前，必须将你的数组进行排序！否则会出现错误的结果！

思想 通过与数组内某个元素(array[i])进行比较，如果比之(array[i])小，则搜索的目标一定在该元素(array[i])之前，否则在(array[i])之后，搜索的范围将缩一半！这样来提搞效率！

 

首先定义一个接口，以后的Search类型都实现这个接口，这样才能不遗漏各种类型的search方法：

 

 public interface SearchUtil {public int search(byte[] array,byte target);public int search(char[] array,char target);public int search(short[] array,short target);public int search(int[] array,int target);public int search(long[] array,long target);public int search(float[] array,float target);public int search(double[] array,double target);public int search(Comparable[] array,Comparable target);}

 

然后用实现类实现以上接口：

 

public class BinarySearch implements SearchUtil{private static SearchUtil search;public static SearchUtil getInstance(){if(null==search)return new BinarySearch();elsereturn search;}//all the functions of basic data type parameters are the same//so i just give a comment in one of thempublic int search(byte[] array,byte target){if(array==null||array.length==0)return -1;//the start index,using for reducing the range for searchingint start=0;//the end index,using for reducing the range for searchingint end=array.length-1;//the index of the element which we will compare to the targetint middle=0;//if start<=end means that we have search all the elementswhile(start<=end){//every time we use the element which in the middle of the start and end to compare with targetmiddle=(start+end)/2;if(array[middle]<target)//if the element is smaller than the target we will search //the part from middle+1 to end start=middle+1;else if(array[middle]==target)//if the element equals the target, just return the index-middlereturn middle;else//if the element is larger than the target we will search //the part from start to middle-1 end=middle-1;}//at last because we use this sentence "middle=(start+end)/2"//this always make the element not just in the middle of the start and end,but just one element front//for example: if start=1 end=2 the middle will be 1 so the 2 is never used//so we must fix itif(middle<array.length-1){middle++;if(array[middle]==target)return middle;}return -1;}public int search(char[] array,char target){if(array==null||array.length==0)return -1;int start=0;int end=array.length-1;int middle=0;while(start<=end){middle=(start+end)/2;if(array[middle]<target)start=middle+1;else if(array[middle]==target)return middle;elseend=middle-1;}if(middle<array.length-1){middle++;if(array[middle]==target)return middle;}return -1;}public int search(short[] array,short target){if(array==null||array.length==0)return -1;int start=0;int end=array.length-1;int middle=0;while(start<=end){middle=(start+end)/2;if(array[middle]<target)start=middle+1;else if(array[middle]==target)return middle;elseend=middle-1;}if(middle<array.length-1){middle++;if(array[middle]==target)return middle;}return -1;}public int search(int[] array,int target){if(array==null||array.length==0)return -1;int start=0;int end=array.length-1;int middle=0;while(start<=end){middle=(start+end)/2;if(array[middle]<target)start=middle+1;else if(array[middle]==target)return middle;elseend=middle-1;}if(middle<array.length-1){middle++;if(array[middle]==target)return middle;}return -1;}public int search(long[] array,long target){if(array==null||array.length==0)return -1;int start=0;int end=array.length-1;int middle=0;while(start<=end){middle=(start+end)/2;if(array[middle]<target)start=middle+1;else if(array[middle]==target)return middle;elseend=middle-1;}if(middle<array.length-1){middle++;if(array[middle]==target)return middle;}return -1;}public int search(float[] array,float target){if(array==null||array.length==0)return -1;int start=0;int end=array.length-1;int middle=0;while(start<=end){middle=(start+end)/2;if(array[middle]<target)start=middle+1;else if(array[middle]==target)return middle;elseend=middle-1;}if(middle<array.length-1){middle++;if(array[middle]==target)return middle;}return -1;}public int search(double[] array,double target){if(array==null||array.length==0)return -1;int start=0;int end=array.length-1;int middle=0;while(start<=end){middle=(start+end)/2;if(array[middle]<target)start=middle+1;else if(array[middle]==target)return middle;elseend=middle-1;}if(middle<array.length-1){middle++;if(array[middle]==target)return middle;}return -1;}public int search(Comparable[] array,Comparable target){if(array==null||array.length==0)return -1;int start=0;int end=array.length-1;int middle=0;if(target==null){//null is smaller the any object which is not null//so when the element is not null,we just search front itwhile(start<=end){middle=(start+end)/2;if(array[middle]==null)return middle;elseend=middle-1;}if(middle<array.length-1){middle++;if(array[middle]==null)return middle;}}else{int rs=0;while(start<=end){middle=(start+end)/2;if(array[middle]==null)//null is smaller the any object which is not null//we make the rs<0 ,so we just search behind itrs=-1;elsers=array[middle].compareTo(target);if(rs<0)start=middle+1;else if(rs==0)return middle;elseend=middle-1;}if(middle<array.length-1){middle++;if(array[middle]==null)return -1;else if(array[middle].compareTo(target)==0)return middle;}}return -1;}}