Today while I was solving a problem based on dfs, I found something unusual and I am still in doubt, how did that happen!

Problem Link : http://codeforces.me/problemset/problem/463/D

My AC Solution : http://codeforces.me/contest/463/submission/13773175

Problem Faced : In my solution, I have used an array a[1123][10] to take input but in the second test case provided by judge, n = 66 and k = 4 , so my program is going to access some memory location at a[3][65] which is certainly out of bound! That's why I wonder, how my solution got AC?

Positive suggestions are welcome :)