Would you guys suggest me how to strong my DSA i.e. Data structures and Algorithms. Where to start? Whether I deep dive into all the Data structures and Algorithms available or just the required one which are majorly used. Also what is the thinking strategy that what DSA can be used in which type of problems.

Help me with this one!!! Whatever the logic I'm applying, time limit gets exceeded in the Test Case 4. This is my solution — https://codeforces.com/contest/1328/submission/167650940 I've tried without storing the values and directly printing it but the result was same — Time Limit Exceeded.

Could anyone help me with this problem? I have done the part where it checks the number if it contains 4 and 7 it prints YES else it prints NO. But if the number contains only digit 4 or 7 such as 444 or 777 then it should print NO but my code is printing YES. I need help with this part.