On a plane are n points (xi, yi) with integer coordinates between 0 and 106. The distance between the two points with numbers a and bis said to be the following value: 
(the distance calculated by such formula is called Manhattan distance).
We call a hamiltonian path to be some permutation pi of numbers from 1 to n. We say that the length of this path is value 
.
Find some hamiltonian path with a length of no more than 25 × 108. Note that you do not have to minimize the path length.
The first line contains integer n (1 ≤ n ≤ 106).
The i + 1-th line contains the coordinates of the i-th point: xi and yi (0 ≤ xi, yi ≤ 106).
It is guaranteed that no two points coincide.
Print the permutation of numbers pi from 1 to n — the sought Hamiltonian path. The permutation must meet the inequality 
.
If there are multiple possible answers, print any of them.
It is guaranteed that the answer exists.
5 0 7 8 10 3 4 5 0 9 12
4 3 1 2 5
In the sample test the total distance is:
(|5 - 3| + |0 - 4|) + (|3 - 0| + |4 - 7|) + (|0 - 8| + |7 - 10|) + (|8 - 9| + |10 - 12|) = 2 + 4 + 3 + 3 + 8 + 3 + 1 + 2 = 26
题目大意：给出平面上的n个点$\left(x_i,y_i\right)$，定义$dist\left(i,j\right)=\left|x_i-x_j\right|+\left|y_i-y_j\right|$，求1~n的一个排列p，使得$\sum_{i=1}^{n-1}dist\left(p_i,p_{i+1}\right)\leq 2.5\times 10^9$。
将所有点按纵坐标分组，纵坐标1~1000一组，1001~2000一组，依此类推，每组都按横坐标排序，然后按之字形走，易证结果一定不会超过要求的值。
代码是用C#的LINQ写的，看不懂就算了。。
代码在此。
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