We will hold AtCoder Beginner Contest 220.

- Contest URL: https://atcoder.jp/contests/abc220
- Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210926T2100&p1=248
- Duration: 100 minutes
- Number of Tasks: 8
- Writer: blackyuki, kyopro_friends, Nyaan, physics0523, QCFium, sugarrr, YoshikaMiyafuji
- Rated range: ~ 1999

The point values will be 100-200-300-400-500-500-600-600.

We are looking forward to your participation!

This contest clashes with a codechef contest, can it be postponed/preponed to remove the clash ?

Wtf is F, did you guys run out of problems?

yep , simple f, i do f in 5 minutes and still strugling on e

I was $$$3^{rd}$$$ at the 10-15 minute mark in the leaderboard cuz of F lol. Used the exact same code for Tree Distances II CSES just changing " " to "\n"...

F is the reason that you should read all the problems

How can I say, I solved F but didn't solve E before the end of the contest...

why is this DP solution wrong for problem D?

My Approach:dp[i][j] = no. of ways to get j at i-th index after doing some operations. and let's assume instead of popping two elements and then pushing, we reach at an index i doing such operations and all the prev indices are processed, so final ans will be to find the no. of ways at last index.

to get j at ith index, our ans will only depend on no. of ways to get 'x' at index i-1 such that (v[i]+x)%10 == j or (v[i]*x)%10 == j and no other values than x should affect no. of ways to get j at ith index. so summation of the no. of ways of to get each such x should get the no. of ways to get j at ith index.

When you are incrementing dp[i][j], you have to add dp[i-1][last] twice in case both the conditions are satisfied.

thanks i totally missed that. it works now.

How do I increase my speed? I solved 4 problems and my rank is 2245. XYZ solved 4 problems and rank is 1578.

Can someone provide tags for all the problems?

Well, at least F has a different output format. https://cses.fi/problemset/task/1133

ok fine change

`' '`

to`'\n'`

PS: It works on CSES with

`'\n'`

as the separator anyway so you can submit the Atcoder submission exactly to CSES and it'll AC.Did anyone else also just look at F and open CSES on the next click?

the bonus task of F: 791D - Bear and Tree Jumps

can anyone share his recursive approach for problem d.

at any state ,we are possible two move,we should go both move and calculate the total value. here my submission, if you are any query ask me ..https://atcoder.jp/contests/abc220/submissions/26150901

thanks . i got your soln but how can we do it in one pass.

it's dp.when one valid move are finished ,you must hit to the base case. you remember that ,you will be hit in the base case many more times ,also hit to the same state more times. so you must memorize to the state value.

How would a Top-Down solution look like for abc220_d?

Problem Link: https://atcoder.jp/contests/abc220/tasks/abc220_d

Their official editorial has a bottom-up solution. I have understood and solved it with the bottom-up approach. I was just curious how would top solution will look like for this problem?

I tried, but there seems that I have to invert the modulo operator in here to get to the top-down solution. the DP states and the base case look intuitive, the DP call is not so much.

https://atcoder.jp/contests/abc220/submissions/26150901