A. Math Problem
Your math teacher gave you the following problem:
There are n segments on the x-axis, [l1;r1],[l2;r2],…,[ln;rn]. The segment [l;r] includes the bounds, i.e. it is a set of such x that l≤x≤r. The length of the segment [l;r] is equal to r−l.
Two segments [a;b] and [c;d] have a common point (intersect) if there exists x that a≤x≤b and c≤x≤d. For example, [2;5] and [3;10] have a common point, but [5;6] and [1;4] don't have.
You should add one segment, which has at least one common point with each of the given segments and as short as possible (i.e. has minimal length). The required segment can degenerate to be a point (i.e a segment with length zero). The added segment may or may not be among the given n segments.
In other words, you need to find a segment [a;b], such that [a;b] and every [li;ri] have a common point for each i, and b−a is minimal.
Input
The first line contains integer number t (1≤t≤100) — the number of test cases in the input. Then t test cases follow.
The first line of each test case contains one integer n (1≤n≤105) — the number of segments. The following n lines contain segment descriptions: the i-th of them contains two integers li,ri (1≤li≤ri≤109).
The sum of all values n over all the test cases in the input doesn't exceed 105.
Output
For each test case, output one integer — the smallest possible length of the segment which has at least one common point with all given segments.
Example
input
4
3
4 5
5 9
7 7
5
11 19
4 17
16 16
3 12
14 17
1
1 10
1
1 1
output
2
4
0
0
Note
In the first test case of the example, we can choose the segment [5;7] as the answer. It is the shortest segment that has at least one common point with all given segments.
题意
给你若干个区间，然后你需要找到一个长度最小的区间，覆盖住所有的区间，问你这个区间最小是多少
题解
我们考虑l最大能够是多少，r最小能够是多少，然后我们就发现 l = min(a[i].r,l),r = max(a[i].l,r)，然后最后取个差值就好
代码
#include<bits/stdc++.h>
using namespace std;
vector<pair<int,int> >A;
void solve(){
int n;cin>>n;
A.clear();
for(int i=0;i<n;i++){
int x,y;
cin>>x>>y;
A.push_back(make_pair(x,y));
}
sort(A.begin(),A.end());
int ll = A[0].first,lr=A[0].second;
int rl = A[0].first,rr=A[0].second;
for(int i=0;i<n;i++){
lr = min(lr,A[i].second);
rl = max(rl,A[i].first);
}
// cout<<lr<<" "<<rl<<endl;
if(lr>=rl){
cout<<"0"<<endl;
}else{
cout<<rl-lr<<endl;
}
}
int main(){
int t;
scanf("%d",&t);
while(t--){
solve();
}
}