Dalgerok's blog

By Dalgerok, history, 2 years ago,

• +176

 » 2 years ago, # |   +2 thanks for tutorial and your effort
 » 2 years ago, # |   -27 Thank you for fast editorial!
•  » » 2 years ago, # ^ |   +8 Please stop this shit
 » 2 years ago, # |   -37 Thanks for the quick editorial.
 » 2 years ago, # | ← Rev. 2 →   +65 Nice Problem Fast System Testing Quick Editorial Overall Great contest :)
•  » » 2 years ago, # ^ | ← Rev. 2 →   +4 + First time to be Specialist . :)
•  » » » 2 years ago, # ^ |   +3 Ya :)
•  » » 2 years ago, # ^ |   +12 Wasn't perfect — placement of B and D was wrong
 » 2 years ago, # |   0 Here's how i did problem D. 52982122Just sort the array according to the below comparator. bool comp( pair< int ,int > a, pair< int, int > b){ if(a.first + b.second > a.second + b.first) return true; else return false; } Proof: Let there be two pairs a and b. The dissatisfaction is i*(a1 + a2 — b1 — b2 ) + n*(b1 + b2) — a1 — a2 . We have to just consider the i term as rest are constant terms. Sort it according to a1 — b1 > a2 — b2
•  » » 2 years ago, # ^ |   0 Thx! Easy to understand !!
•  » » 10 months ago, # ^ |   0 the formula given is Ai(i -1) + Bi(N-i). So if you take two pairs A and B. then Ai and Bi for A and B are A1,A2 and B1,B2 respectively. Then total dissatisfaction due to both would be A1(i-1) + A2(N-i) + B1(i-1) + B2(N-i). So this should reduce to (A1 — A2 + B1 — B2)i + constants. Now Please tell how did you get A1+A2-B1-B2 for 'i' term.
 » 2 years ago, # | ← Rev. 4 →   +4 I used divide and conquer in E. Let $f(l,r)$ equals answer for segment $[l;r]$ and $half = (l+r)/2$ then $f(l,r) = f(l,half) + f(half+1,r) - min(arr[half], arr[half+1]) * (n - max(arr[half], arr[half+1]) + 1)$.
•  » » 2 years ago, # ^ |   0 Oh! Egor Letov is alive!
•  » » 14 months ago, # ^ | ← Rev. 2 →   0 Hi, I went through your submission but couldn't understand the intuition behing Divide and Conquer.Could you please explain your intuition behind it ....Thanks in advance !
•  » » » 14 months ago, # ^ |   +1 I used the same approach as him so I will try to explain it. Let say we want to find the answer for an array A. Now imagine that for some of the ranges (l, r) the two halves of A always belong to different components. For example the array A is: 2 4 6 2 7 3 and the range is (2, 3) or (6, 10). For these type of ranges we can just calculate the answer of each half seperately and sum them up. However this is not always the case since the exist some ranges for which the right point of the first half is connected to the left point of the second half. Say the range (2, 6) or (1, 10) in the example. How to handle these cases? Well we will sum them up similar to what we do with the first case. Now the answer will contain some invalid components — for each range similar to (2, 6) or (1, 10) we have counted the middle component twice. Now what we have to do is to substract from the answer the number of ranges for which the two border points remain the same. This is the meaning of the last term in his recurrence equation.
•  » » » » 14 months ago, # ^ |   0 Thanks !!
 » 2 years ago, # | ← Rev. 2 →   -12 This is boolshit))
•  » » 2 years ago, # ^ |   +16 Have you coded your solution? I'm sure that it is wrong. Firstly, I think that $m_{i, i} \neq m_{i, j}$. Secondly, you can't compute the answer by multiplying the probabilities (your last sentence), because they are not independent.
•  » » » 2 years ago, # ^ |   +2 You are right! I am stupid))
 » 2 years ago, # |   -6 For problem D, you don't really need to sort by index. "array d in non-decreasing order". I solved without sorting D.
•  » » 2 years ago, # ^ |   +8 Yes, It is already sorted :)
 » 2 years ago, # |   0 It is very thankful for brilliant tutorial.
 » 2 years ago, # |   0 can somebody explain me problem c and I have seen some solution like (calc(R) — calc(L — 1) + mod) % mod here he is adding mod, why? if we are not adding mod then 6 test case fail.please help me. Thank u
•  » » 2 years ago, # ^ |   +5 It depends on your language. Languages like C and C++ don't return values between $0$ and $MOD-1$ while taking mod of a negative number. Instead they return the 'negative mod'. $-5mod4$ should be $3$, but $-1$ is returned. While $-1$, is correct, it's not what we want. So, we add an extra $MOD$ and take mod again to ensure the result lies between $0$ and $MOD-1$. Adding an extra mod should always be done if you're subtracting 2 numbers and taking their mods.
•  » » » 2 years ago, # ^ |   +9 Thanks bro
 » 2 years ago, # |   0 Please add Solutions when published editorials. it's helped a lot.
 » 2 years ago, # | ← Rev. 2 →   0 For problem C, this is my solution https://codeforces.com/contest/1151/submission/53005511 The solution uses the logic given in the editorial. I have tried placing MOD in all possible location and still not getting the correct answer. Anyone help? :)
•  » » 2 years ago, # ^ |   0 Anyone please :)
•  » » » 2 years ago, # ^ |   0 In your fun(), it's enough if you just calculate the pow(2, i) without the mod. By subtracting, what you're essentially doing is just dividing the variable x by 2. So taking mod on the variable x would affect the loop because modular division is not similar to modular addition or subtraction where you can take mod wherever and it wouldn't affect the answer. So, using pow(2, i) on line 39 and removing line 50 would be the way to go.
•  » » » » 2 years ago, # ^ |   +1 Yeah thanks bro :)
•  » » 2 years ago, # ^ | ← Rev. 2 →   0 The problem probably lies in how you implemented the power() function. The way you iterate it is not obvious to me, and I'm not sure y = y/2 is the right way to do it.
 » 2 years ago, # |   0 Can anybody explain to me how to work a code in B
•  » » 15 months ago, # ^ |   0 i used sets to get rows since set contains only unique values hence even if there are multiple elements only unique values get in set but i need index of those numbers too hence i created map,int> to contain the index of element ( where map[{0,4}] means what is the index of 4 in row 0) then i build recursion to solve further, i was passing a vector to keep track of index so if i get xor>0 i can pass the track movement to global vector and return true ,further if i get true i don't need to to check for other indexes and can end that recursionhere's my submission https://codeforces.com/contest/1151/submission/85774757 if you have any doubts regarding this feel free to ask
 » 2 years ago, # | ← Rev. 3 →   +4 DalgerokIN E editorial, Shouldn't it be:we must find the number of pairs (l,r) such that ai is not on the range [l,r] and ai−1 is on the range [l,r]. instead of:we must find the number of pairs (l,r) such that ai is on the range [l,r] and ai−1 is not on the range [l,r].
•  » » 2 years ago, # ^ |   +3 No, because $b_i$ must be $1$ and $b_{i-1}$ must be $0$.
•  » » » 2 years ago, # ^ |   0 Got it thanks :)
 » 2 years ago, # |   0 The explanation of problem B is not helpful! Can anyone explain it?
•  » » 2 years ago, # ^ |   0 first take element from first column from each row and take their XORs. If xor!=0, simply print the index of elements and exit. If xor==0, then iterate all elements of the table. If in a given row, current element is different from element in first column, then , if we replace the first element with this element, our xor will become non-zero.
•  » » » 2 years ago, # ^ |   0 thanks mate
•  » » » 2 years ago, # ^ |   0 thanks for this simple and easy explaination. can you plz explain problem C also??
•  » » » » 2 years ago, # ^ |   0 to find sum of numbers from L to R, you need to do (sum of first m numbers in this sequence)- (sum of first L-1 numbers in the sequence). This is a simple observation, you can check this by taking first 10 natural numbers.Now, to find sum of first L-1 numbers , you need to count the number of odd no. and number of even nos. till (L-1). To count both, start a loop from i=1 , double it on every iteration while increasing count of odd and even numbers alternatively. But, keep in mind the last count which you will add, which may not be power of 2.finally, suppose, you got 'a' odd numbers and 'b' even numbers. then sum= a*a + b*(b+1) (simple AP series sum formula) you can do similar calculation for first M numbers.
•  » » » » » 2 years ago, # ^ |   0 http://codeforces.com/contest/1151/submission/53007448check my code to see how I have done it.
•  » » » » » » 2 years ago, # ^ |   0 Thank you!!☺
 » 2 years ago, # |   0 The last problem is so awesome! By the way, is there some problem that has similar "style" to the last one? I mean, its not dp on the book, it's like... creativeness on how to define dp state?
 » 2 years ago, # | ← Rev. 2 →   0 Can anyone please tell me for problem 'B' why I am getting WA on test 9 while I ran same thing on my machine and it's shows correct output? link While after that I tried doing same thing using for loop and guess what, go AC!! link
•  » » 2 years ago, # ^ |   0 Anyone?? :/
 » 2 years ago, # |   +1 For F, how do we use matrix exponentiation when the dp has more than 1 dimension?
•  » » 2 years ago, # ^ |   0
•  » » 2 years ago, # ^ |   +5 When $f[i][j]$ can be represented as a linear combination of $f[i - 1][k]$ for some $k$'s, it is possible to define a transition matrix from $f[i - 1]$ to $f[i]$. Let this matrix be $M$. Then by multiplying $M^n$ with the vector $f[i]$ you can jump to $f[i + n]$.
 » 2 years ago, # |   0 Here's my submission for B. https://codeforces.com/contest/1151/submission/52967808Could someone explain the judge's verdict of XOR being less than 0 for testcase 24?
•  » » 2 years ago, # ^ |   0 It means the sequence you provided as the answer arrives at a XOR value of $0$, which implies that it is not a valid sequence.
 » 2 years ago, # |   0 For the problem D. Why my solution https://codeforces.com/contest/1151/submission/53019943 is getting runtime error.
•  » » 2 years ago, # ^ |   0 when I change the compare function now it gives WA. what is the problem now and before. https://codeforces.com/contest/1151/submission/53019888
•  » » » 2 years ago, # ^ |   0 Anyone Please :)
•  » » » » 2 years ago, # ^ |   0 I don't really know about JAVA, but in C++, for a false comparison, you have to return 0. Why don't you try changing the -1 to 0.
•  » » » » » 2 years ago, # ^ |   0 https://codeforces.com/contest/1151/submission/52980095 This is the same code written in c++ but it is also giving runtime error on test case 8.
•  » » » » » » 2 years ago, # ^ |   0 I tried out your code, with a single change. I changed your compare statement, from f>=0 to f>0 and it worked.Runtime Error — https://codeforces.com/contest/1151/submission/53027297As to why this happens, I am clueless. Maybe someone can give some insight to this.
•  » » » » » » » 2 years ago, # ^ | ← Rev. 2 →   0 Thanks. But someone please tell why it was not working previously.
 » 2 years ago, # |   0 In Problem B we can also use RANDOM SHUFFLE!!!.We can Random Shuffle all the elements in each row and then check the xor for each column that whether it is greater than zero or not.P.S.-I have applied random shuffle 200 times.Luckily it passes all the tests :PHere's link to my solution : 53025553
•  » » 2 years ago, # ^ |   0 You may want to actually calculate the probability of getting false negative in the worst case (only one element is different in one of the rows). It might be surprisingly small.
•  » » 2 years ago, # ^ |   0 That was just a lucky try. I might get WA on submitting the same solution
 » 2 years ago, # |   0 Can anyone provide a prerequisite for understanding solution of problem C for mortals like me? I can't even ...
•  » » 2 years ago, # ^ | ← Rev. 2 →   0 You may take a look at my solution of C. Not exactly the approach of the editorial (in that the editorial is more straight forward in counting the size of each group), but it could possibly help you get a better perspective.
•  » » » 2 years ago, # ^ |   0 Wow ! very detailed answer ! Thank you.
•  » » » 2 years ago, # ^ |   0 Amazing... Better Than editorial Thanks for posting
 » 2 years ago, # |   0 I have done following in problem C. Function calculates the sum in set till number n.ev — next even sequence start od — next odd sequence startthen for each iteration, I calculate start and end of that sequence and calculate their sum by AP. It is giving wrong answer on test case 1 1e18. Is there an overflow ? I cannot find the bug in function calc.code link CODE#include #include #include using namespace std; #include #include using namespace __gnu_pbds; template using ordered_set = tree, rb_tree_tag, tree_order_statistics_node_update>; // s.order_of_key(x); // gives order of x in the set #define For(i,x,n) for(long long i=x;i>l>>r; cout<<(calc(r)-calc(l-1)+MOD)%MOD; //cout<<"\nTime used = "<(clock())/(CLOCKS_PER_SEC)<<"s"< hm; ll i; for(i=2 ; i*i<=15000002 ; i++) if(isprime[i]==0){ for(ll j=2*i ; j<=15000001 ; j+= i) if(isprime[j]==0) isprime[j]=i; isprime[i]=i; hm[i] = cc; cc++; } for( ; i<15000002 ; i++) if(isprime[i]==0) isprime[i]=i,hm[i]=cc,cc++; } ll choose(ll n,ll k) { if(k==0) return 1; return (n* choose(n-1,k-1))/k; } void showArray(ll a[], ll n){ For(i,0,n){ cout< eps && fabs(y) > eps) { if (x > y) x -= floor(x / y) * y; else y -= floor(y / x) * x; } return x + y; } ll power(ll x,ll n) { if(n==0) return 1; else if(n%2 == 0) //n is even return (power((x*x)%MOD,n/2))%MOD; else //n is bal return (x*power((x*x)%MOD,(n-1)/2))%MOD; } ll power1(ll x,ll n) { ll num = 1; For(i,0,n){ num = (num*x)%MOD; } return num; } 
 » 2 years ago, # |   0 I have found a solution with O(1) complexity for Problem C. See 53051961Can anyone tell is it really a O(1) complexity? (I am just new to algorithm and I don't know is it right)Thank you :)
•  » » 2 years ago, # ^ |   0 No, it is $O(\log{N})$.
 » 2 years ago, # |   +6 Can someone explain the approach behind E problem ? Whats the logic for calculating f(l,r) ?
 » 2 years ago, # |   0 For problem D .By changing the compare statement, from f>0 to f>=0 my code gets runtime error.Runtime Error — https://codeforces.com/contest/1151/submission/53027297As to why this happens, I am clueless.Someone please tell why it started giving runtime error.
•  » » 2 years ago, # ^ |   0 Someone Please reply :(
 » 2 years ago, # |   0 i still cant understand problem c can anyone explain me?
 » 2 years ago, # |   0 For Problem E — The editorial states "using technique contribution to the sum". What is this technique ??
•  » » 2 years ago, # ^ |   0
 » 2 years ago, # |   0 Great Editorial!
 » 2 years ago, # |   0 My solution for Problem C works fine for smaller size of input but it failed for larger value. But, I'm pretty sure that I took the modulo correctly. Tried a lot to debug but failed. Could you please give a look in my code?
•  » » 2 years ago, # ^ | ← Rev. 2 →   0 You should multiply by inverse modulo values instead of dividing on them.
•  » » » 2 years ago, # ^ |   0 Are you talking about the lines even /= 3;, odd /= 3;?
•  » » » » 2 years ago, # ^ |   0 Yes
•  » » » » » 2 years ago, # ^ | ← Rev. 2 →   0 Actually, in those lines, I was finding the length of total odd and even numbers not the sum itself.
 » 2 years ago, # |   0 why i am getting wrong output for test case 21 in problem B 53825407 waiting for response.
 » 2 years ago, # |   0 In problem B there is 'dp' tag on it. Is there any dp solution of it? I'm looking for...
 » 2 years ago, # | ← Rev. 2 →   0 Couldn't understand div2E can anyone please explain ??? Even the question isn't clear as how is f(l,r) calculated and what is the use of values of nodes...??
 » 2 years ago, # |   0 can any one help me with problem C. I am getting wrong answer for big values. https://codeforces.com/contest/1151/submission/57858024
 » 19 months ago, # | ← Rev. 2 →   0 Can someone tell me how to solve B using dp?