Codeforces Beta Round 84 (Div. 1 Only)

Solutions for Codeforces Beta Round 84 (Div. 1 Only) (contest 109). 5/5 problems verified against sample I/O. Difficulty range: 1000-2700.

5 items

Codeforces Beta Round 84 (Div. 1 Only)

Type: Div. 1 | Problems: 5 | Verified: 5/5 | Rating range: 1000-2700 | Time: 11m 6s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Lucky Sum of Digits	1000	brute-force, implementation	2m 22s	✓
B	Lucky Probability	1900	brute-force, probabilities	2m 23s	✓
C	Lucky Tree	1900	dp, dsu, trees	2m 23s	✓
D	Lucky Sorting	2000	constructive-algorithms, sortings	1m 47s	✓
E	Lucky Interval	2700	brute-force, math	2m 11s	✓

Practice › Codeforces Solutions › Codeforces Beta Round 84 (Div. 1 Only) ›

CF 109A - Lucky Sum of Digits

We need to construct the smallest possible lucky number whose digits add up to a given value n. A lucky number may contain only digits 4 and 7. For example, 447 is valid because every digit is either 4 or 7, while 45 is invalid because digit 5 appears.

Practice › Codeforces Solutions › Codeforces Beta Round 84 (Div. 1 Only) ›

CF 109B - Lucky Probability

We are asked to calculate the probability that if Petya and Vasya each pick an integer randomly from their respective intervals, the interval between the two chosen numbers contains exactly k lucky numbers. Lucky numbers are those containing only the digits 4 and 7.

Practice › Codeforces Solutions › Codeforces Beta Round 84 (Div. 1 Only) ›

CF 109C - Lucky Tree

We are given a tree with n vertices where each edge has a positive weight. Some edges are considered "lucky" if their weight consists only of the digits 4 and 7.

Practice › Codeforces Solutions › Codeforces Beta Round 84 (Div. 1 Only) ›

CF 109D - Lucky Sorting

We are given an array of positive integers, and we want to sort it in non-decreasing order. The twist is that we can only swap elements if at least one of the two numbers involved is lucky. A lucky number is defined as a number containing only the digits 4 and 7.

Practice › Codeforces Solutions › Codeforces Beta Round 84 (Div. 1 Only) ›

CF 109E - Lucky Interval

We are given an interval of consecutive integers starting at a and having length l. For every number x, define F(x) as the count of lucky digits inside its decimal representation. Only digits 4 and 7 are considered lucky.