Codeforces Round #FF (Div. 2) 447A - DZY Loves Hash（模拟）

A. DZY Loves Hash

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

DZY has a hash table with p buckets, numbered from 0 to p - 1.
He wants to insert n numbers, in the order they are given, into the hash table. For the i-th
number xi, DZY
will put it into the bucket numbered h(xi),
where h(x) is the hash function. In this problem we will assume, that h(x) = x mod p.
Operation a mod b denotes taking a remainder after division a by b.

However, each bucket can contain no more than one element. If DZY wants to insert an number into a bucket which is already filled, we say a "conflict" happens. Suppose the first conflict happens right after the i-th
insertion, you should output i. If no conflict happens, just output -1.

Input

The first line contains two integers, p and n (2 ≤ p, n ≤ 300).
Then n lines follow. The i-th of them contains an
integer xi (0 ≤ xi ≤ 109).

Output

Output a single integer — the answer to the problem.

Sample test(s)

input

10 5
0
21
53
41
53

output

4

input

5 5
0
1
2
3
4

output

-1

AC代码：

#include <stdio.h>
#include <string.h>
int main(){
int n,p,b[310],a,i,num,flag;
while(~scanf("%d%d",&p,&n)){
flag=0;
num=-1;
memset(b,0,sizeof(b));
for(i=0;i<n;i++){
scanf("%d",&a);
a%=p;
if(!flag){
if(!b[a])
b[a]++;
else{
flag=1;
num=i+1;
}
}
}
printf("%d\n",num);
}
return 0;
}