答案都对，但全WA，求大佬指点

wanxuhang @ 2023-08-04 22:34:14

#include<bits/stdc++.h>
using namespace std;
long long a[1000005];
int f1(int left,int right,long long x){
    if (left>right) return left;
    int mid=(left+right)/2;
    if (a[mid]==x) return f1(left,mid-1,x);
    else if (a[mid]>x) return f1(left,mid-1,x);
    else if (a[mid]<x) return f1(mid+1,right,x);
}
int main(){
    int n,q;
    cin>>n>>q;
    for (int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }
    for (int i=1;i<=q;i++){
        long long x;
        cin>>x;
        int ans=f1(1,q,x);
        if(x!=a[ans]) printf("-1 ");
        else(printf("%d ",ans));
    }

    return 0;
} 

by dfindsinfvidsnv @ 2023-08-05 14:59:22

mid不要-1吧，本蒟蒻也不太清楚

我的代码

#include<bits/stdc++.h>
using namespace std;
long long a[1000001],n,m,x;
int find(int x,int l,int r){
    if(x==a[l])return l;
    if(l>=r) return -1;
    int mid=l+((r-l)>>1);
    if(a[mid]>=x)return find(x,l,mid);
    else return find(x,mid+1,r);
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    cin>>n>>m;
    for(int i=1;i<=n;i++){
        cin>>a[i];
    }while(m--){
        cin>>x;
        cout<<find(x,1,n)<<" ";
    }
    return 0;
}

by wanxuhang @ 2023-08-06 22:57:17

@yang_yi_bo 感谢，我再研究一下

by wo_hen_la @ 2023-08-07 11:40:55

@wanxuhang

最简单的代码

#include<bits/stdc++.h>
using namespace std;
map<long long,int> a;
int main()
{
    long long n,m,b;
    cin>>n>>m;
    for(long long i=0;i<n;i++){
        scanf("%d",&b);
        if(a[b]==0){
            a[b]=i+1;
        }
    }
    while(m--){
        scanf("%d",&b);
        if(a[b]==0) printf("%d ",-1);
        else printf("%d ",a[b]);
    }
    return 0;
}

by wanxuhang @ 2023-08-07 11:49:32

@wo_hen_la 感谢，我找到问题了