Java算法2--二分搜索法

一、二分搜索法實現類

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、二分搜索法測試類

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));
    }
}