1.寻找符合条件的第一个数&最后一个数

package alg;
import bilibili.chapter16.Array;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
import java.util.Scanner;
public class Search {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(),q = sc.nextInt();
        int []a = new int[100010];
        for(int i=0;i<n;i++) a[i]=sc.nextInt();
        System.out.println(Arrays.toString(a));
        while(q-->0){
            int k = sc.nextInt();
            int l = 0,r = n-1;
            while (l<r){
                int mid = l+r>>1;
                if(a[mid]>=k) r = mid;
                else l = mid + 1;
            }
            System.out.println(l);
            int left = l;
            if(a[l]!=k) System.out.println("-1 -1");
            else {
                 l = 0;
                 r = n - 1;
                 while (l<r){
                     int mid = l+r+1>>1;
                     if(a[mid]<=k) l = mid;
                     else r = mid - 1;

                 }
                System.out.println(left+" "+r);

            }
        }
    }
}

2.浮点数二分

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double x = sc.nextDouble();
        double l = -10000,r = 10000;
        while(r - l >1e-8){
            double mid = (l+r)/2;
            if(mid*mid*mid>=x) r = mid;
            else l = mid;
        }
        System.out.printf("%.6f",r);

    }
}