1041 Be Unique（20 分）
Being unique is so important to people on Mars that even their lottery is designed in a unique way. The rule of winning is simple: one bets on a number chosen from [1,10
4
]. The first one who bets on a unique number wins. For example, if there are 7 people betting on { 5 31 5 88 67 88 17 }, then the second one who bets on 31 wins.
Input Specification:
Each input file contains one test case. Each case contains a line which begins with a positive integer N (≤10
5
) and then followed by N bets. The numbers are separated by a space.
Output Specification:
For each test case, print the winning number in a line. If there is no winner, print None instead.
Sample Input 1:
7 5 31 5 88 67 88 17
Sample Output 1:
31
Sample Input 2:
5 888 666 666 888 888
Sample Output 2:
None
解题思路：
用类似打表的方法，统计每个数出现的次数。按输出顺序遍历，当有次数为1的数时，输出，没有就输出None。
#include<cstdio>
const int maxn=1e5+10;
int book[maxn]={0} ;
int a[maxn];
int main(){
int n,x;
scanf("%d",&n);
for(int i=0;i<n;i++){
scanf("%d",&x);
a[i]=x;
book[x]++;
}
int ans=-1;
for(int i=0;i<n;i++){
if(book[a[i]]==1){
ans=a[i];
break;
}
}
if(ans==-1) printf("None\n");
else printf("%d\n",ans);
return 0;
}