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;
}