Visiting a Friend

题意翻译

题目描述 小猪准备拜访一位朋友。它的家在数轴上0的位置，它朋友的家在m的位置。小猪通过传送在轴上移动。 当使用传送时，小猪应位于一些特定的传送点之一，并选择目的地。对每个传送点分别有一个限制，传送点不能把小猪送到限制点的右方。 形式上讲，一个位于x，限制是y的传送点可以把小猪从点x传送到闭区间 [x,y]上的任意整点。 判断小猪在仅适用使用传送的情况下能否到达朋友家。 输入输出格式 输入格式： 第一行两个整数n和m（1<=n<=100,1<=m<=100），代表传送点的数量和朋友的家的坐标。 接下来n行包含传送点的信息。 这些行中的第i行包含两个整数ai和bi，0<=ai<=bi<=m，其中ai代表第i个传送点的坐标，bi代表第i个传送点的限制 保证ai>=ai-1（2<=i<=n）。 输出格式： 如果小猪只用传送就可以抵达朋友家，那么输出"YES"，否则输出"NO"。 对每个字符，输出其大写或者其小写都可以。（译者：也就是说"YES"和"Yes"甚至"yEs"都算对。） translated by Pantw

题目描述

Pig is visiting a friend. Pig's house is located at point $ 0 $ , and his friend's house is located at point $ m $ on an axis. Pig can use teleports to move along the axis. To use a teleport, Pig should come to a certain point (where the teleport is located) and choose where to move: for each teleport there is the rightmost point it can move Pig to, this point is known as the limit of the teleport. Formally, a teleport located at point $ x $ with limit $ y $ can move Pig from point $ x $ to any point within the segment $ [x;y] $ , including the bounds. Determine if Pig can visit the friend using teleports only, or he should use his car.

输入输出格式

输入格式

The first line contains two integers $ n $ and $ m $ ( $ 1<=n<=100,1<=m<=100 $ ) — the number of teleports and the location of the friend's house. The next $ n $ lines contain information about teleports. The $ i $ -th of these lines contains two integers $ a_{i} $ and $ b_{i} $ ( $ 0<=a_{i}<=b_{i}<=m $ ), where $ a_{i} $ is the location of the $ i $ -th teleport, and $ b_{i} $ is its limit. It is guaranteed that $ a_{i}>=a_{i-1} $ for every $ i $ ( $ 2<=i<=n $ ).

输出格式

Print "YES" if there is a path from Pig's house to his friend's house that uses only teleports, and "NO" otherwise. You can print each letter in arbitrary case (upper or lower).

输入输出样例

输入样例 #1

3 5
0 2
2 4
3 5

输出样例 #1

YES

输入样例 #2

3 7
0 4
2 5
6 7

输出样例 #2

NO

说明

The first example is shown on the picture below: Pig can use the first teleport from his house (point $ 0 $ ) to reach point $ 2 $ , then using the second teleport go from point $ 2 $ to point $ 3 $ , then using the third teleport go from point $ 3 $ to point $ 5 $ , where his friend lives. The second example is shown on the picture below: You can see that there is no path from Pig's house to his friend's house that uses only teleports.