The only difficulty of this problem is the array size. There is no idea given in the problem. I use 1,000,000 is as array size for both sequence and subsequence. Those who are using Turbo C/C++ 3.0 IDE would not able to make the large array normally. They need to use malloc or new. The best way to use large array is, make program and debug with small array and at the time of submit just change the array size. The online judge support large array(64k).