CF558A

Amr lives in Lala Land. Lala Land is a very beautiful country that is located on a
coordinate line. Lala Land is famous with its apple trees growing everywhere.
Lala Land has exactly n apple trees. Tree number i is located in a position xi and
has ai apples growing on it. Amr wants to collect apples from the apple trees. Amr
currently stands in x = 0 position. At the beginning, he can choose whether to go right
or left. He'll continue in his direction until he meets an apple tree he didn't visit
before. He'll take all of its apples and then reverse his direction, continue walking
in this direction until he meets another apple tree he didn't visit before and so on.
In the other words, Amr reverses his direction when visiting each new apple tree.
Amr will stop collecting apples when there are no more trees he didn't visit in the
direction he is facing.
What is the maximum number of apples he can collect?
Input
The first line contains one number n (1 ≤ n ≤ 100), the number of apple trees in Lala Land.
The following n lines contains two integers each xi, ai
( - 105 ≤ xi ≤ 105, xi ≠ 0, 1 ≤ ai ≤ 105), representing the position of the i-th tree and
number of apples on it.
It's guaranteed that there is at most one apple tree at each coordinate.
It's guaranteed that no tree grows in point 0.
Output
Output the maximum number of apples Amr can collect.
Examples
Input
2
-1 5
1 5
Output
10
Input
3
-2 2
1 4
-1 3
Output
9
Input
3
1 9
3 5
7 10
Output
9
Note
In the first sample test it doesn't matter if Amr chose at first to go left or right.
In both cases he'll get all the apples.
In the second sample test the optimal solution is to go left to x =  - 1, collect apples
from there, then the direction will be reversed, Amr has to go to x = 1, collect apples
from there, then the direction will be reversed and Amr goes to the final tree x =  - 2.
In the third sample test the optimal solution is to go right to x = 1, collect apples from
there, then the direction will be reversed and Amr will not be able to collect anymore
apples because there are no apple trees to his left.

题意：有n课苹果树，已知每棵苹果树的位置和苹果数，一人从x=0处出发，方向向左或者向右，但没遇到一棵
苹果树，他会摘下苹果，然后调转方向。问他最后最多能取到多少苹果。

解题： 如果正负位置数量相同，那么都可取，如果不相同，那么少的一边全取，多的一边取离0近的.

#include <cstdio>
#include <algorithm>
#define N 105

using namespace std;

struct note {
	int x; int cnt;
}a[N];

int cmp(struct note a, struct note b)
{
	return a.x < b.x;
}

int main()
{
	int n;
	struct note a[N];
	while (scanf("%d", &n) != EOF)
	{
		int ans = 0;
		int cnt1 = 0, cnt2 = 0;
		for (int i = 1; i <= n; i++)
		{
			scanf("%d%d", &a[i].x, &a[i].cnt);
			if (a[i].x > 0)
				cnt1++;
			else
				cnt2++;
		}
		sort(a + 1, a + n + 1, cmp);
		
		if (cnt1 == cnt2)
		{
			for (int i = 1; i <= n; i++)
				ans += a[i].cnt;
		}
		else if (cnt1 > cnt2)
		{
			for (int i = 1; i <= cnt2 * 2 + 1; i++)
				ans += a[i].cnt;
		}
		else
		{
			for (int i = n; i > n - 2 * cnt1 - 1; i--)
				ans += a[i].cnt;
		}
		printf("%d\n", ans);
	}
	return 0;
}