Java算法2--二分搜索法

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一、二分搜索法实现类

public class BinarySearch {    public static int BinarySearch1(int a[],int x,int n)    {        int left=0;int right=n-1;        while(left<=right)        {            int middle=(left+right)/2;            if(x==a[middle]) return middle;            if(x>a[middle]) left=middle+1;            else right=middle-1;        }        return -1;    }}    public static int BinarySearch2(int a[],int x,int n)    {        int left=0;int right=n-1;        while(left<right-1)        {            int middle=(left+right)/2;            if(x<a[middle]) right=middle;            else left=middle;        }        if(x==a[left]) return left;        return -1;    }    public static int BinarySearch3(int a[],int x,int n)    {        int left=0;int right=n-1;        while(left+1!=right)        {            int middle=(left+right)/2;            if(x>=a[middle]) left=middle;            else right=middle;        }        if(x==a[left]) return left;        return -1;    }    public static int BinarySearch4(int a[],int x,int n)    {        if(n>0&&x>=a[0])        {            int left=0;int right=n-1;            while(left<right)            {                int middle=(left+right)/2;                if(x<a[middle]) right=middle-1;                else left=middle;            }            if(x==a[left]) return left;        }        return -1;    }    public static int BinarySearch5(int a[],int x,int n)    {        if(n>0&&x>=a[0])        {            int left=0;int right=n-1;            while(left<right)            {                int middle=(left+right+1)/2;                if(x<a[middle]) right=middle-1;                else left=middle;            }            if(x==a[left]) return left;        }        return -1;    }    public static int BinarySearch6(int a[],int x,int n)    {        if(n>0&&x>=a[0])        {            int left=0;int right=n-1;            while(left<right)            {                int middle=(left+right+1)/2;                if(x<a[middle]) right=middle-1;                else left=middle+1;            }            if(x==a[left]) return left;        }        return -1;    }    public static int BinarySearch7(int a[],int x,int n)    {        if(n>0&&x>=a[0])        {            int left=0;int right=n-1;            while(left<right)            {                int middle=(left+right+1)/2;                if(x<a[middle]) right=middle;                else left=middle;            }            if(x==a[left]) return left;        }        return -1;    }}

二、二分搜索法测试类

public class BinarySearchTest {    public static void main(String agrs[])    {        int[] a=new int[]{5,17,21,45,69,84,105};        //System.out.print(BinarySearch.BinarySearch1(a,5,a.length));                //System.out.print(BinarySearch.BinarySearch1(a,105,a.length));        //System.out.print(BinarySearch.BinarySearch1(a,3,a.length));        //System.out.print(BinarySearch.BinarySearch1(a,120,a.length));        //System.out.print(BinarySearch.BinarySearch1(a,17,a.length));    }}

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