using namespace std;

int main() {
    int n;
    cin >> n;
    int a[n];
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    int t;
    cin >> t;
    while (t-- > 0) {
        int x;
        cin >> x;
        int l = 0, r = n - 1;
        while (l <= r) {
            int m = l + (r - l) / 2;
            if (a[m] <= x) {
                l = m + 1;
            } else {
                r = m - 1;
            }
        }
        if (r >= 0 && a[r] == x) {
            cout << r + 1 << " ";
        } else {
            cout << -1 << " ";
        }
    }
    return 0;
}

歪解 哈希表加快读

import java.util.*;
import java.io.*;
public class Main {
	static StreamTokenizer st = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
	static PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    public static void main(String[] args) throws Exception{ 
    	int n = Int();
    	HashMap<Integer,Integer> hm = new HashMap<>();
    	for(int i = 1; i<= n;i++) {
    		hm.put(Int(),i);
    	}
    	int t = Int();
    	for(int i = 1; i<= t;i++) {
    		pw.print(hm.getOrDefault(Int(), -1)+" ");
    	}
    	pw.flush();
    }
    public static int Int() throws Exception{
    	st.nextToken();
    	return (int)(st.nval);
    }
    }

import java.io.*;
import java.util.*;
import java.lang.*;
import java.util.regex.*;
import java.math.*;
public class Main {
    static PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    static StreamTokenizer st = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    static BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
    static List<List<Integer>>res=new ArrayList<>();
    static int n,m;
    public static void main(String[] args) throws Exception {
        Scanner sc=new Scanner(System.in);
n=Int();
var arr=new int[n+1];
        for (int i = 1; i <= n; i++) {
            arr[i]=Int();
        }
        m=Int();
        for (int i = 1; i <= m; i++) {
            int x=Int();
        pw.print(  check(arr,x)+" ");
        }
pw.flush();
    }
    public static int check(int[]arr,int x){
        var l=1;
        var r=n;
        while (l<r){
            int mid=(l+r)/2;
            if(arr[mid]>=x)r=mid;
            else
                l=mid+1;
        }
     if(arr[l]!=x)
         return -1;
     else {
         while (arr[l+1]==arr[l])
             l++;
            return l;
        }}
    public static String Line() throws Exception{
        String s = bf.readLine();
        return s;
    }
    public static int Int() throws Exception{
        st.nextToken();
        return (int) st.nval;
    }
    public static long Long() throws Exception{
        st.nextToken();
        return (long) st.nval;
    }
    public static double Double() throws Exception{
        st.nextToken();
        return (double)st.nval;
    }
}

import java.io.*;
import java.util.Arrays;

public class Main {
    static StreamTokenizer st = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter bw = new PrintWriter(new OutputStreamWriter(System.out));
    public static void main(String[] args) throws Exception {
        int n = Int();
        int[] arr = new int[n];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = Int();
        }
        int t = Int();
        //循环查找每一个需要查找的元素
        for (int i = 0; i < t; i++) {
            int key = Int();
            //调用二分查找算法，返回查找结果并输出到输出流中
            int res = binarySearch0(arr, key);
            bw.print((res + 1) + " ");
        }
        //刷新输出流
        bw.flush();
    }
    //读入整数的方法
    public static int Int() throws Exception{
        st.nextToken();
        return (int)(st.nval);
    }
    //二分查找算法
    public static int binarySearch0(int[] a, int key) {
        int low = 0;
        int high = a.length - 1;
        while (low <= high) {
            int mid = (low + high) / 2;
            int midVal = a[mid];
            if (midVal < key)
                low = mid + 1;
            else if (midVal > key)
                high = mid - 1;
            else {
                //进行左右判断，找到第一个等于key的元素并返回
                low = mid;
                if(((mid >0 && mid < a.length - 1) && a[mid - 1] != key && a[mid + 1] != key) || (mid == 0 && a[mid + 1] != key) || (mid == a.length - 1 && a[mid - 1] != key)) return mid;
                //如果不是第一个等于key的元素，继续查找下一个元素直到最后一个等于key的元素并返回
                while (low <= high) {
                    mid = (low + high) / 2;
                    midVal = a[mid];
                    if(midVal != key) high = mid - 1;
                    else low = mid + 1;
                }
                return low - 1;
            }
        }
        //未找到等于key的元素
        return -2;
    }
}

public class Main{
    public static void main(String args[]){
    	Scanner in=new Scanner(System.in);
    	int n=in.nextInt();
    	int[] a=new int[n];
    	for(int i=0;i<n;i++) {
    		a[i]=in.nextInt();
    	}
    	int t=in.nextInt();
    	while(t-->0) {
    		int x=in.nextInt();
    		int l=0,r=n-1;
    		while(l<=r) {
    			int m=l+(r-l)/2;
    			if(a[m]<=x) {
    				l=m+1;
    			}else {
    				r=m-1;
    			}
    		}
    		if(r>=0&&a[r]==x) {
    		System.out.print(r+1+" ");
    		}else {
    			System.out.print(-1+" ");
    		}
    	}
    }
}