笔记

if (check(mid)) L = mid ，则 mid = L + R + 1 >> 1

if (check(mid)) R = mid ，则 mid = L + R  >> 1

题目 

 

#include<bits/stdc++.h>
using namespace std;

int n, q;
int a[100010];
int b[10010];
typedef pair<int, int> PII;

void search_binary(int x)
{
	int mid = n >> 1;
	int l = 0, r = n-1;
	while(l < r)
	{
		if(a[mid] >= x) r = mid;
		else l = mid + 1;
		mid = l + r >> 1;
	}
	
	if(a[r] == x)
		cout<<r<<' ';
	else
	{
		cout<<-1<<' '<<-1<<'\n';
		return;
	}
		
	l = 0;
	r = n-1;
	while(l < r)
	{
		mid = l + r + 1 >> 1;
		if(a[mid] <= x) l = mid;
		else r = mid - 1;
	}
	cout<<l<<'\n';
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	
	cin>>n>>q;
	for(int i=0;i<n;++i) cin>>a[i];
	for(int i=0;i<q;++i) cin>>b[i];
	
	for(int i=0;i<q;++i) search_binary(b[i]);
	
	return 0;
}