二分查找

 1/**
 2 * 2分查找
 3 *
 4 * @author wangy
 5 * @version 1.0
 6 * @date 2020/6/5 / 14:23
 7 */
 8public class BinSearch {
 9
10    public static int binSearch(ArrayList<Integer> list, int key) {
11        Collections.sort(list);
12        int low = 0;
13        int high = list.size() - 1;
14
15        while (low <= high) {
16            int mid = (low + high) / 2;
17            if (list.get(mid) > key) {
18                high = mid - 1;
19            } else if (list.get(mid) < key) {
20                low = mid + 1;
21            } else {
22                return mid;
23            }
24        }
25        return -1;
26
27    }
28
29    public static void main(String[] args) {
30        ArrayList<Integer> al = new ArrayList<>(Arrays.asList(3, 43, 23, 83, 33, 63, 93, 103, 53));
31        Collections.sort(al);
32        System.out.println(Arrays.toString(al.toArray()));
33
34        int i = BinSearch.binSearch(al, 33);
35        System.out.println(i);
36
37        System.out.println(Collections.binarySearch(al, 33));
38    }
39}