800*A. Line Trip（模拟）

Problem - 1901A - Codeforces

#include<bits/stdc++.h>
using namespace std;
//#define int long long
const int N=2e5+5;
int n,x,a[N]; 
void solve(){
	scanf("%d%d",&n,&x);
	for(int i=1;i<=n;i++){
		scanf("%d",&a[i]);	
	}
	int res=0;
	a[0]=0;
	for(int i=1;i<=n;i++){
		res=max(res,a[i]-a[i-1]);
	}
	printf("%d\n",max(res,2*(x-a[n])));
}
signed main(){
	int t=1;
	scanf("%d",&t);
	while(t--) solve();
	return 0;
}