#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{
	ios::sync_with_stdio(false);
	int n, m, x, y;
	cin >> n >> m;
	vector<int>a;
	vector<int>b;
	for (int i = 0; i < n; i++)
	{
		cin >> x;
		a.push_back(x);
	}//第一组数
    
	for (int i = 0; i < m; i++)
	{
		cin >> y;
		b.push_back(y);
	}//第二组数
    
	for (int i = 0; i < m; i++)
	{
		int p = lower_bound(a.begin(),a.end(), b[i]) - a.begin();//二分查找
        
		if(b[i]!=a[p])//判断输出，但这里没搞明白...
			cout << "-1";
        else
            cout<<p+1<<" ";
	}
	return 0;
}

我想请教一下该怎么改？