C. Maximal Intersection
time limit per test
3 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
You are given n
segments on a number line; each endpoint of every segment has integer coordinates. Some segments can degenerate to points. Segments can intersect with each other, be nested in each other or even coincide.
The intersection of a sequence of segments is such a maximal set of points (not necesserily having integer coordinates) that each point lies within every segment from the sequence. If the resulting set isn't empty, then it always forms some continuous segment. The length of the intersection is the length of the resulting segment or 0
in case the intersection is an empty set.
For example, the intersection of segments [1;5]
and [3;10] is [3;5] (length 2), the intersection of segments [1;5] and [5;7] is [5;5] (length 0) and the intersection of segments [1;5] and [6;6] is an empty set (length 0
).
Your task is to remove exactly one segment from the given sequence in such a way that the intersection of the remaining (n−1)
segments has the maximal possible length.
Input
The first line contains a single integer n
(2≤n≤3⋅105
) — the number of segments in the sequence.
Each of the next n
lines contains two integers li and ri (0≤li≤ri≤109) — the description of the i
-th segment.
Output
Print a single integer — the maximal possible length of the intersection of (n−1)
remaining segments after you remove exactly one segment from the sequence.
Examples
Input
Copy
4 1 3 2 6 0 4 3 3
Output
Copy
1
Input
Copy
5 2 6 1 3 0 4 1 20 0 4
Output
Copy
2
Input
Copy
3 4 5 1 2 9 20
Output
Copy
0
Input
Copy
2 3 10 1 5
Output
Copy
7
Note
In the first example you should remove the segment [3;3]
, the intersection will become [2;3] (length 1). Removing any other segment will result in the intersection [3;3] (length 0
).
In the second example you should remove the segment [1;3]
or segment [2;6], the intersection will become [2;4] (length 2) or [1;3] (length 2), respectively. Removing any other segment will result in the intersection [2;3] (length 1
).
In the third example the intersection will become an empty set no matter the segment you remove.
In the fourth example you will get the intersection [3;10]
(length 7) if you remove the segment [1;5] or the intersection [1;5] (length 4) if you remove the segment [3;10].
问去掉一段区间重合的最大区间长度。
set，multiset的用法：
begin()：返回第一个元素的位置；
end():返回最后一个元素的下一个位置
rbegin():返回逆序的第一个位置（就是正序的第一个位置）
代码：
#include<bits/stdc++.h>
using namespace std;
const int maxn=300010;
multiset<int>a,b;///先定义两个set可重复
int L[maxn],R[maxn];
int main()
{
int n;
scanf("%d",&n);
for(int i=1;i<=n;i++){
scanf("%d%d",&L[i],&R[i]);
a.insert(L[i]);
b.insert(R[i]);
}
int ans=0;
for(int i=1;i<=n;i++){
a.erase(a.find(L[i]));
b.erase(b.find(R[i]));
ans=max(ans,*(b.begin())-*(a.end()));
a.insert(L[i]);
b.insert(R[i]);
}
printf("%d\n",ans);
}