[POI2006]ZAB-Frogs

题目描述

A scourge of frogs destroying all the crop has started in Byteotia. A farmer named Byteasar has decided to fight the vermin with peculiar "scarefrogs", that he has set up at certain points of his field. While moving from one place to another, every frog tries to keep as far of them as possible, i.e. maximizes the distance to the closest scarefrog. The field that belongs to Byteasar has rectangular shape. The frogs leap in directions parallel to the field's sides and their leaps are unitary (of length 1). The scarefrogs-distance, for a given frog's route, is the minimum of all distances from all scarefrogs at all inter-leap-points of the route. Byteasar already knows the most common starting and destination points of the frogs' routes, therefore he experiments with various deployments of the scarefrogs. He asks you for help, namely he would like you to write a programme that calculates the maximum (over all routes) scarefrogs-distance for a given deployment of scarefrogs - which we call in short the frogshold distance. TaskWrite a programme that: reads from the standard input the size of the field, the coordinates of the screfrogs and the source and target position of a frog,determines the frogshold distance (the maximum scarefrogs-distance a frog may achieve while still being able to reach the target point)writes the square of this number to the standard output. 给定一个网格图，其中有一些坏点，要求使起点到终点的路径上的所有点到离该点最近的坏点的最小距离距离最大，求这个最大值。

输入输出格式

输入格式

The first line of the input contains two integers: $w_x$ and $w_y$ separated by a single space - the breadth and length of the field ($2 \le w_x, w_y \le 1000$). The second line of the input contains four integers: $p_x$, $p_y$, $k_x$ and $k_y$ separated by single spaces; $(p_x, p_y)$ is the initial position of the frog, $(k_x, k_y)$is the target (final) position of the frog ($1 \le p_x, k_x \le w_x$, $1 \le p_y, k_y \le w_y$). The third line of the standard input contains one integer $n$ - these are the coordinates of the ith scarefrog ($1 \le n \le w_x \cdot w_y$). No two scarefrogs occupy the same position and none of them is at the point $(p_x, p_y)$ nor $(k_x, k_y)$.

输出格式

In the first and only line of the standard output one integer should be written, namely the square of the frogshold distance. If the frog cannot avoid leaping directly on some scarefrog the result is 0.

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