二分查找

public class BinarySearch {
    //递归
    public static int findData(int[] a, int b, int beginIndex, int endIndex) {
        if(a.length == 0 || a == null) {
            return 0;
        }
        int length = (beginIndex + endIndex)/2;
        if(b == a[length]) {
            return length;
        }else if(b < a[length]) {
            return findData(a, b,  beginIndex, length-1);
        }else {
            return findData(a, b, length+1, endIndex);
        }
    }
    
    //非递归
    public static int findData2(int[] a, int des) {
        int left = 0 ;
        int right = a.length -1;
        while(left <= right) {
            int middle = (left + right)/2;
            if(des == a[middle]) {
                return middle;
            }
            if (des > a[middle]) {
                left = middle + 1;
            }
            if(des < a[middle]) {
                right = middle - 1;
            }
        }
        return -1;
    }
    
    //测试
    public static void main(String[] args) {
        int a[] = {1,5,8,9,8};
        System.out.println(a.length);
        int b = 9;
        int des = 7;
        //int ret = findData(a, b, 0, a.length-1);
        int ret = findData2(a, des);
        System.out.println(ret);
    }

}