#include <iostream>

using namespace std;

long long BinarySearch(long long A[],long long n,long long key)
{

    long long  i=0,j=n-1;
    if(A[0]>key) return 0;
    while(i<=j)
    {
        long long mid=(i+j)/2;
        if(key>A[mid])
        {
            i=mid+1;
        }
        else if(key<A[mid])
        {
            j=mid-1;
        }
        else if(A[mid]==key)
        {
            return mid+1;
        }

    }
    return i;//没找到返回i
}
int main()
{
    long long n,m;
    cin>>n>>m;
    long long *A=new long long [n];
    long long *B=new long long [m];
    for(long long  i=0;i<n;i++)
    {
        cin>>A[i];
    }
     for(long long  i=0;i<m;i++)
    {
        cin>>B[i];
    }

    for(long long  i=0;i<m;i++)
    {
        long long j=BinarySearch(A,n,B[i]);
       cout<<j<<endl;
    }
    return 0;
}

你这代码……写得也不像向左逼近啊 qwq 如果有多个相等的 A_i，感觉不行吧

参考：

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll mn = 1e5 + 10;
ll n, m, a[mn];
signed main()
{
    ios::sync_with_stdio(false), cin.tie(0);
    cin >> n >> m;
    for (ll i = 1; i <= n; ++i)
    {
        cin >> a[i];
    }
    while (m--)
    {
        ll lf = 1, rf = n, k, ans = 0;
        cin >> k;
        while (lf <= rf)
        {
            ll cf = (lf + rf) >> 1;
            if (a[cf] <= k)
            {
                ans = cf;
                lf = cf + 1;
            }
            else
            {
                rf = cf - 1;
            }
        }
        cout << ans << '\n';
    }
    return 0;
}