for i in range(int(input())):
	a, d, w = int(input()), input().split(), {}
	for i in range(a):
		if d[i] in w:
			w[d[i]].append(i)
		else:
			w[d[i]]=[i]
	a+=1
	for i in w:
		z = w[i]
		for p in range(len(z)-1):
			a = min(a, z[p+1]-z[p])
	if len(d)<a:
		print(-1)
	else:
		print(a+1)