# Hello,World

Hello，这里是一只萌萌哒的OIer

# SuperUserDo

## Problem Statement

Fox Ciel just used the command "sudo" (super-user do) to gain administrative privileges in the UNIX-based operating system on her computer. She now wants to install several new programs. Each program has some dependencies: in addition to the program, the package manager has to install some libraries used by the program.
The package repository contains exactly 1000 libraries. For simplicity, we will number them from 1 to 1000, inclusive.
You are given the information about the dependencies of the programs Fox Ciel wants to install. More precisely, you are given the int[]s A and B, both containing the same number of elements. For each valid i, one of the programs needs all libraries that have numbers between A[i] and B[i], inclusive. Note that the programs may have overlapping dependences: multiple programs may require the same library to be installed. Of course, in such cases it is sufficient to install such a library once.
Calculate and return the total number of libraries that need to be installed.

# [codeforces754D] Fedor and coupons

## 题目大意

$N$个线段，从中选$k$个线段，使得交集最大。

# [poj 1741] Tree

## Description

Give a tree with n vertices,each edge has a length(positive integer less than 1001).
Define dist(u,v)=The min distance between node u and v.
Give an integer k,for every pair (u,v) of vertices is called valid if and only if dist(u,v) not exceed k.
Write a program that will count how many pairs which are valid for a given tree.

# [bzoj 1295][SCOI2009]最长距离

## Description

windy有一块矩形土地，被分为 N*M 块 1*1 的小格子。 有的格子含有障碍物。 如果从格子A可以走到格子B，那么两个格子的距离就为两个格子中心的欧几里德距离。 如果从格子A不可以走到格子B，就没有距离。 如果格子X和格子Y有公共边，并且X和Y均不含有障碍物，就可以从X走到Y。 如果windy可以移走T块障碍物，求所有格子间的最大距离。 保证移走T块障碍物以后，至少有一个格子不含有障碍物。