数的范围 二分

二分 数的范围
一个是找左边界 一个找又边界
l = mid情况下更新时 mid = l + r + 1 >> 1的原因是向下取整 如果不加一 mid = l,更新 l = mid陷入死循环

#include<iostream>
#include <algorithm>
#include <vector>
using namespace std;
const int maxn=100010;
const int INF=2*int(1e9)+10;
#define LL long long
int n, m;
int q[maxn];
int main(){
	cin >> n >> m;
	for(int i = 0; i < n; i++) cin >> q[i];
	while(m--)
	{
		int x;
		cin >> x;
		int l = 0, r = n - 1;
		while(l < r)
		{
			int mid = l + r >> 1;
			if(q[mid] >= x) r = mid;
			else l = mid + 1;
		} 
		if(q[l] != x) cout << "-1 -1" << endl;
		else
		{
			cout << l << " ";
			int l = 0, r = n - 1;
			while(l < r)
			{
				int mid = l + r + 1 >> 1;
				if(q[mid] <= x) l = mid;
				else r = mid - 1;
			}
			cout << l << endl;
		}

	}
	return 0;	
}