简单_二分法算法

package sunfa;//二分法查找public class TestBinSearch {public static void main(String[] args) {/** * 集合必须是排序好的，否则查不到。有多个相同的元素则只返回首先被找到的那一个。 * 参考:java.util.Arrays.binarySearch方法 */int[] arr={1,2,3,4,5,611,6,6,7,8,9};int r=binSearch(arr, 6);System.out.println(r);}public static int binSearch(int a[],int key){int mid = a.length/2;if(key==mid){return mid;}int start=0;int end=a.length-1;while(start<=end){mid = (end-start)/2+start;//避免(start+end)/2超过 int范围if(key<a[mid]){end = mid-1;}else if(key>a[mid]){start=mid+1;}else{return mid;}}return -1;}}