应该算是二分答案+结构体

#include <bits/stdc++.h>
using namespace std;
const int N = 2e5+10;
int a[N];
int n,x;
struct node{
    int number;
    int id;
}b[N];
bool cmp(node x,node y){
    return x.number<y.number;
}
int bs(int k){
    int ans = 0;
    int l=1,r=n;
    while(l<=r){
        int mid = (l+r)>>1;
        if( k>b[mid].number){
            l = mid + 1;
        }else{
            r = mid - 1;
            ans = mid;
            
        }      
    }
    if(b[ans].number == k){
        return ans;
    }else{
        return 0;
    } 
}
int main(){
	cin >> n;
	for(int i =1;i<=n;i++){
		cin >> b[i].number;
        b[i].id = i;
	}
    sort(b+1,b+n+1,cmp);
	int m;
    cin >> m;
    while(m--){
        int x;
        cin >> x;
        cout <<b[bs(x)].id<<endl;
    }
	return 0;
}