二分法的Java实现

    public class TestSearch{
        public static void main(String[] args){
            int[] a= {1, 3, 6, 8, 9, 10, 12, 18, 20, 34 };
            int i=12;
            //System.out.println(search(a,i));
            System.out.println(binarySearch(a,i));
            }
        public static int search(int[] a,int num){
            for(int i=0;i<a.length;i++){
                if(a[i]==num){
                    return i;
                    }
                }
            return -1;
            }
        public static int binarySearch(int[] a,int num){
            if(a.length==0) return -1;
            int startPos=0;
            int endPos=(a.length)-1;
            int m=(startPos+endPos)/2;
            while(a[startPos]<=a[endPos]){
                if(num==a[m]) return m;
                if(num<a[m]){
                    endPos=m-1;
                    }
                if(num>a[m]){
                    startPos=m+1;
                    }
                m=(startPos+endPos)/2;
                }
            return -1;
            }
        }