#include <iostream>
using namespace std;
int a[100005];
int main()
{
    int n, q, x;
    cin >> n;
    for (int i = 1 ; i <= n ; i++)
        cin >> a[i];
    cin >> q;
    for (int i = 1 ; i <= q ; i++)
    {
        cin >> x;
        int l = 1, r = n, mid;
        while (l <= r)
        {
            mid = (l + r) / 2;
            if (a[mid] < x)
                l = mid + 1;
            else if (a[mid] > x)
                r = mid - 1;
            else
                break;
        }
        int first = mid;
        while (a[first] == x)
            first--;
        if (first == mid) 
            first = -1;
        else 
            first++;
        cout << first << " ";
    }
    return 0;
} //代码已AC

#include<bits/stdc++.h>
using namespace std;
int main(){
int a[100000],b,c,d,e;cin>>b;
for(e=1;e<=b;e++)cin>>a[e];
cin>>c;
for(e=1;e<=c;e++){cin>>d;if(a[lower_bound(a+1,a+b+1,d)-a]==d){cout<<lower_bound(a+1,a+b+1,d)-a<<' ';}else cout<<-1<<' ';}
return 0;
}//代码已AC

#include <bits/stdc++.h>
using namespace std;
int a[10000005];
int main()
{
    int n, m, x, l, r, ans;
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    cin >> m;
    for (int i = 1; i <= m; i++){
        cin >> x;
        l = 1;
        r = n;
        ans = -1;
        while (l <= r){
            int mid = (l + r) / 2;
            if (a[mid] >= x){
                if (a[mid] == x)
                    ans = mid;
                r = mid - 1;
            }else{
                l = mid + 1;
            }
        }
        cout << ans << " ";
    }
}

服了呀！8个AC，2个TLE！

#include <iostream>
using namespace std;
int main()
{
    int n,q,x;
    cin>>n;
    int a[n+1];
    for (int i=1;i<=n;i++)cin>>a[i];
    cin>>q;
    for (int i=1;i<=q;i++)
    {
        cin>>x;
        int ans=0;
        for (int j=1;j<=n;j++)
        {
            if (a[j]==x)
            {
                ans++;
                cout<<j<<" ";
                break;
            }
        }
        if (ans==0)cout<<"-1 ";
    }
    return 0;
}

#include <iostream>
#include <algorithm>
using namespace std;
int a[100001],n,q,x;
int main()
{
    cin>>n;
    for (int i=1;i<=n;i++)
        cin>>a[i];
    cin>>q;
    for (int i=1;i<=q;i++)
    {
        cin>>x;
        if (a[lower_bound(a+1,a+n+1,x)-a]==x)
            cout<<lower_bound(a+1,a+n+1,x)-a<<' ';
        else
            cout<<-1<<' ';
    }
}

for (int i=1;i<=q;i++)
{
    cin>>x;
    ans=-1;
    l=1;
    r=n;
    while (l<=r)
    {
        int mid=(l+r)/2;
        if (a[mid]>=x)
        {
            if (a[mid]==x)//这里由于大于等于都算了进去，无法确定是否为x，需再判断一次
            {
                ans=mid;
            }
            r=mid-1;
        }
        else
        {
            l=mid+1;
        }
    }
    cout<<ans<<" ";
}

#include<bits/stdc++.h>
using namespace std;
int a[1000001],n,x;
int Find(int low,int high)
{
	if(a[low]>x||a[high]<x||low>high)
		return -1;
	
	int mid=(low+high)/2;
	if(a[mid]==x)
	{
		if(low==high) //虽然找到 a[mid]=x，但是它不一定是首次出现的，还要继续找 
			return mid;
		else
			return Find(low,mid);
	}
	else if(a[mid]<x)
		return Find(mid+1,high);
	else
		return Find(low,mid-1);
}
int main()
{
	int i,q;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		scanf("%d",&a[i]);
	
	scanf("%d",&q);
	
	while(q--)
	{
		scanf("%d",&x);	
		printf("%d ",Find(1,n));
	}
	

	return 0;
}

#include <cstdio>
using namespace std;
int main(){
    int n,x,q,l,r,mid,pos,a[100001];
    scanf("%d",&n);
    for(int i=1;i<=n;i++)scanf("%d",&a[i]);
    scanf("%d",&q);
    for(int i=1;i<=q;i++){
        l=1,r=n,pos=-1;
        scanf("%d",&x);
        while(l<=r){
            mid=(l+r)/2;
            if(a[mid]==x)pos=mid;
            a[mid]>=x?r=mid-1:l=mid+1;
        }
        printf("%d%c",pos,' ');
    }
    printf("\n");
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
int n,q,x;
int a[100005];
int main(){
    cin>>n;
    for (int i=1;i<=n;i++){
        cin>>a[i];
    }
    sort(a+1,a+n+1);
    cin>>q;
    while (q--){
        cin>>x;
        int l=1,r=n;
        while (l<=r){
            int mid=(l+r)>>1;
            if (a[mid]>=x){//大于等于可以保证找到第一次出现的位置
                r=mid-1;
            }else{
                l=mid+1;
            }
        }
        cout<<(a[l]==x?l:-1)<<" ";//特判找不到的情况
    }
    return 0;
}

鼓励大家写题解，但注意题解格式。

给代码两端加上这个会舒服一些

```cpp

你的代码

```

这个点在键盘的左上角tab上面那个键，注意切换输入法

#include<iostream>
using namespace std;
int main()
{
    int n;
    cin>>n;//这是一个注释
    return 0;
} 

请注意严禁抄袭题解，写题解不要只放代码，需加上你的思路或代码注释。

抄袭题解一经发现直接取消成绩。