3.整数二分
模板
package base;public class Bsearch {public int binary_search1(int l, int r){while (l<r){int mid = (l+r+1)>>1;if(check(mid)) l=mid;else r = mid-1;}return l;}public int binary_search2(int l, int r){while (l<r){int mid = (l+r)>>1;if (check(mid)) r = mid;else l=mid+1;}return l;}public boolean check(int mid){return false;}
}例题：
package test;import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;public class Test1 {public static void main(String[] args){BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));try{System.out.println("输入数组长度:");int n = Integer.parseInt(bf.readLine());//定义数组int a[] = new int[n];for(int i = 0;i<n;i++){System.out.println("在数组中添加第"+(i+1)+"个数据:");a[i] = Integer.parseInt(bf.readLine());}//定义查询个数System.out.println("输入要查询元素的个数:");int q = Integer.parseInt(bf.readLine());//开始查找while(q-->0){System.out.println("输入要查询元素值:");int x = Integer.parseInt(bf.readLine());binary_search(n,a,x);}}catch(IOException e){e.printStackTrace();}}/*n:数组长度a[]:数组x：要查询的数x*/public static void binary_search(int n,int[] a,int x){//定义指针int l = 0,r = n-1;while(l<r){//确定左边界int mid = (l+r)>>1;if(a[mid]>=x) r=mid;else l=mid+1;}if(a[l]!=x){System.out.println("-1 -1");return;}else System.out.print(l+" ");//确定右边界l = 0;r = n-1;while(l<r){int mid = (l+r+1)>>1;if(a[mid]<=x) l = mid;else r=mid-1;}System.out.println(l);}}