题解 | 二分查找

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(), m = sc.nextInt();
        int[] nums = new int[n];
        for (int i = 0; i < n; i++) nums[i] = sc.nextInt();
        int left = 0, right = n - 1;
        while (left <= right) {
            int mid = (left + right) / 2;
            if (nums[mid] < m) left = mid + 1;
            else if (nums[mid] > m) right = mid - 1;
            else {
                System.out.println(mid);
                return;
            }
        }
        System.out.println(-1);
        sc.close();
    }
}