【Educational Codeforces Round 16】Codeforces 710B Optimal Point on a Line

You are given n points on a line with their coordinates xi. Find the
point x so the sum of distances to the given points is minimal. Input

The first line contains integer n (1?≤?n?≤?3·105) — the number of
points on the line.

The second line contains n integers xi (?-?109?≤?xi?≤?109) — the
coordinates of the given n points. Output

Print the only integer x — the position of the optimal point on the
line. If there are several optimal points print the position of the
leftmost one. It is guaranteed that the answer is always the integer.

第一眼看到可能想当然地以为是平均数，但其实这是错的。
对于奇数个点，应该取中位数，对于偶数个点，应该取最中间两个数之间的任意一点。
证明：如果移动x距离，则有多于一半的点距离增加x，少于一半的点距离减少x，结果变差。

#include<cstdio>
#include<algorithm>
using namespace std;
int a[300010];
int main()
{int i,j,k,n;scanf("%d",&n);for (i=1;i<=n;i++)scanf("%d",&a[i]);sort(a+1,a+n+1);printf("%d\n",a[(n+1)/2]);
}