1141

题目描述

There is a sequence S consisting of N numbers, where N is an odd number. All numbers in this sequence appear even number times, except one showing up odd number times, which we call unique number. For example, in the sequence {3, 4, 4, 9, 3, 5, 3, 3, 9}, the number 5 is the unique number. Now you are required to work out the unique number for given sequence. 

输入

Input file consists of several cases.The first line of each case contains a number N. Each of the next N lines contains only one number Si. We guarantee that the number N is no more than 100,000, and Si is no more than 2^31.

输出

For each case, just return the unique number in one line.

样例输入

9344935339

样例输出

5

提示

Try O(n) algorithm.

来源

2012.03

#include<stdio.h>#include<string.h>int comp(const void *a, const void *b){    return *(int *)a - *(int *)b;}int main(){  int i,n;   while(scanf("%d",&n)!=EOF)  {   int num=0;   int a[n],m;   for(i=0;i<n;i++)   scanf("%ld",&a[i]);   qsort(a,n,sizeof(a[0]),comp);for (i=0;i<n;i++){if (i==0||a[i]!=a[i-1]) {//第一个和每一个新出现的第一个if (num%2) {printf("%d\n",a[i-1]);break;}num=1;//每一个新出现数的第一个记为1}else num++;}}     return 0;}