HDU 2095 find your present (2) Find the number that appears only once

Find your present (2) Time Limit: 2000/1000 MS (Java/others) memory limit: 32768/1024 K (Java/Others)
Total submission (s): 15349 accepted submission (s): 5821


Problem descriptionin the New Year party, everybody will get a "special present ". now it's your turn to get your special present, a lot of presents now putting on the desk, and only one of them will be yours. each present has a card number on it, and your present's card number will be the one that different from all the others, and you can assume that only one number appear odd times. for example, there are 5 present, and their card numbers are 1, 2, 3, 2, 1.so your present will be the one with the card number of 3, because 3 is the number that different from all the others.
Inputthe input file will consist of several cases.
Each case will be presented by an integer N (1 <= n <1000000, and N is odd) at first. following that, n positive integers will be given in a line, All integers will smaller than 2 ^ 31. these numbers indicate the card numbers of the presents. n = 0 ends the input.
Outputfor each case, output an integer in a line, which is the card number of your present.
Sample Input

51 1 3 2 231 2 10

 
Sample output

32

Data is a bit watery, and non-conforming data appears in pairs, so some people use bitwise operations ^ to

I used map for sorting and found that the memory limit, 1024*1024/4 = 262144 cannot meet the 10 ^ 6

Therefore, only map is allowed.

#include <stdio.h>#include <algorithm>#include <map>using namespace std;int main(){int n,i,a;map<int,int>my;map<int,int>::iterator it;while(scanf("%d",&n),n){for(i=0;i<n;i++) {scanf("%d",&a);my[a]++;}for(it=my.begin();it!=my.end();it++){if(it->second==1){printf("%d\n",it->first);break;}}my.clear();}return 0;}