水个c++ ac代码

#include<bits/stdc++.h>
using namespace std;
#define int long long
int n,q,a[100100];
//l<r`最终l==r l即为最终答案 需要缩小范围l=mid+1 r=mid-1(不然会死循环)
//l<r-1 最终l与r相邻 不需要缩小范围 但是最后要判断l和r是否符合
void ch1(int l,int r,int x){
    int mid=(l+r)/2;
    while(l<r-1){
        mid=(l+r)/2;
        if(a[mid]>=x){
           r=mid;
        }
        else l=mid;
    }
    if(x==a[l])cout<<l<<endl;
    else if(x==a[r])cout<<r<<endl;
    else cout<<-1<<endl;
   
}
void ch2(int l,int r,int x){
    int mid=(l+r)/2;
    while(l<r-1){
        mid=(l+r)/2;
        if(a[mid]<=x){
            l=mid;
        }
        else r=mid;
    }
    if(a[r]==x)cout<<r<<endl;
    else if(a[l]==x)cout<<l<<endl;
    else cout<<-1<<endl;
}
void ch3(int l,int r,int x){
    int mid=(l+r)/2;
    while(l<r){
        mid=(l+r)/2;
        if(a[mid]>=x){
            r=mid;
        }
        else l=mid+1;
    }
    if(a[r]>=x)cout<<r<<endl;
    else cout<<-1<<endl;
}
void ch4(int l,int r,int x){
    int mid=(l+r)/2;
    while(l<r){
        mid=(l+r)/2;
        if(a[mid]>x){
            r=mid;
        }
        else l=mid+1;
    }
    if(a[l]>x)cout<<l<<endl;
    else cout<<-1<<endl;
}
signed main(){
    cin>>n>>q;
    for(int i=1;i<=n;i++){
    cin>>a[i];
}
    for(int i=1;i<=q;i++){
        int op,l,r,x;
        cin>>op>>l>>r>>x;
        if(op==1){
            ch1(l,r,x);
        }
        if(op==2){
            ch2(l,r,x);
        }
        if(op==3){
            ch3(l,r,x);
        }
        if(op==4){
            ch4(l,r,x);
        }
    }
        return 0;
}

蓝桥云课AC代码 JAVA: 判断条件应为区间，选那种二分看最终点在区间的左端还是右端。

int l=0,r=n;
while(l<r){
  int mid=(l+r)>>1;
  if(判断条件) r=mid;
  else l=mid+1;
}
out.println(l);
out.close();

int l=0,r=n;
while(l<r){
  int mid=(l+r+1)>>1;
  if(判断条件) r=mid-1;
  else l=mid;
}
out.println(l);
out.close();

import java.util.*;
import java.util.StringTokenizer;
import java.io.*;

public class Main {

	public static void main(String[] args) {
		//数据读入
		int n=in.nextInt();
		int q=in.nextInt();
		int[] a=new int[n+1];
		for(int i=1;i<=n;i++){
			a[i]=in.nextInt();
		}
		
		while(q-->0){
			int op=in.nextInt(),l=in.nextInt(),r=in.nextInt(),x=in.nextInt();
			if(op==1) out.println(getL(a,l,r,x));
			else if(op==2) out.println(getR(a,l,r,x));
			else if(op==3) out.println(lower_bound(a,l,r,x));
			else out.println(upper_bound(a,l,r,x));
		}
		out.close();
	}
	
	

	private static int upper_bound(int[] a, int l, int r, int x) {
		if(a[r]<=x) return -1;
		while(l<r) {
			int mid=(l+r)/2;
			if(a[mid]>x) r=mid;
			else l=mid+1;
		}
		return l;
	}



	private static int lower_bound(int[] a, int l, int r, int x) {
		if(a[r]<x) return -1;
		while(l<r) {
			int mid=(l+r)/2;
			if(a[mid]>=x) r=mid;
			else l=mid+1;
		}
		return l;
	}



	private static int getR(int[] a, int l, int r, int x) {
		while(l<r) {
			int mid=(l+r+1)/2;
			if(a[mid]>x) r=mid-1;
			else l=mid;
		}
		if(a[l]!=x) return -1;
		else return l;
	}



	private static int getL(int[] a, int l, int r, int x) {
		while(l<r) {
			int mid=(l+r)/2;
			if(a[mid]>=x) r=mid;
			else l=mid+1;
		}
		if(a[l]!=x) return -1;
		else return l;
	}



	static FastReader in=new FastReader();
	static PrintWriter out=new PrintWriter(System.out);
	static class FastReader{
		static BufferedReader br;
		static StringTokenizer st;
		FastReader(){
			br=new BufferedReader(new InputStreamReader(System.in));
		}
		String next() {
			String str="";
			while(st==null||!st.hasMoreElements()) {
				try {
					str=br.readLine();
				}catch(IOException e) {
					throw new RuntimeException(e);
				}
				st=new StringTokenizer(str);
			}
			return st.nextToken();
		}
		int nextInt() {
			return Integer.parseInt(next());
		}
		double nextDouble() {
			return Double.parseDouble(next());
		}
		long nextLong() {
			return Long.parseLong(next());
		}
	}
	
}