Codeforces Round ＃649 (Div. 2)——A. XXXXX

Topic link ：https://codeforces.com/problemset/problem/1364/A

Title Description ： When only the beginning and end of the data string can be deleted , Find the longest , Can not be x The length of the substring divisible .

Their thinking ： greedy （ During the input process , When sum cannot be x Divisible time , Take the length of the substring for comparison and update （ l = max（ l,max（ i,n - i ）））i Is the first length on the left （ Similarly, the number on the right is deleted ）,n-i Is the length of the right tail （ Similarly, the number on the left is deleted ）.

Code ：

#include<iostream>
#include<algorithm>
using namespace std;
int num[100005];
int main()
{
    
	int t;
	cin >> t;
	while (t--)
	{
    
		int n, x;
		cin >> n >> x;
		int l = -1, sum = 0;
		for (int i = 1; i <= n; i++)
		{
    
			cin >> num[i];
			sum += num[i];
			if (sum % x)
				l = max(l, max(i, n - i));
		}
		cout << l << endl;
	}
	return 0;
}