2023.9.14 整数二分排序

# 二分

## 整数二分

~~~c++
//区间[l,r]被划分成[l,mid]和[mid+1,r]时使用
int test01(int l,int r)
{
    while(l<r)
    {
        int mid = (l+r)/2;
        bool check(int mid);//check判断mid是否满足x性质
        if(check(mid)) r = mid;//mid满足，即要找的x在[l,mid]区间内
        else l = mid +1;//mid不满足，即要找的x在[mid+1,r]区间内
    }
    return 1;
}
//区间[l,r]被划分成[l,mid-1]和[mid,r]时使用
int test02(int l,int r)
{
    while(l<r)
    {
        int mid = (1+r+1)/2;//mid - 1 = (l+r)/2;
        bool check(mid);
        if(check(mid)) l = mid;
        else r = mid-1;
    }
}
~~~

~~~c++
#include <iostream>
using namespace std;
const int N = 10e6+10;
int m, n;
int q[N];

int main()
{
    cin >> n>>m;
    for (int i = 0; i < n; i++)  cin >> q[i];
    
    while (m--)
    {
        int x; cin >> x;
        int l = 0;
        int r = n - 1;
        while (l < r)
        {
            int mid = (l + r)/2;
            if (q[mid] >= x) r = mid;
            else l = mid + 1;
        }//判断第一种边界情况
        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)/2;
                if (q[mid] <= x) l = mid;
                else r = mid - 1;
            }//判断第二种边界情况
            cout << l << endl;
        }
    }
    return 0;
}