Codeforces Round 848 (Div. 2)

Solutions for Codeforces Round 848 (Div. 2) (contest 1778). 3/6 problems verified against sample I/O. Difficulty range: 800-2600.

6 items

Codeforces Round 848 (Div. 2)

Type: Div. 2 | Problems: 6 | Verified: 3/6 | Rating range: 800-2600 | Time: 10m 59s

Problem Name Rating Tags Solve Time Verified
A Flip Flop Sum 800 greedy, implementation 3m 21s ✗
B The Forbidden Permutation 1300 greedy, math 2m 31s ✓
C Flexible String 1600 bitmasks, brute-force, strings 1m 23s ✓
D Flexible String Revisit 2100 combinatorics, dp, math 1m 38s ✗
E The Tree Has Fallen! 2500 bitmasks, dfs-and-similar, math 1m 32s ✓
F Maximizing Root 2600 dfs-and-similar, dp, graphs 34s ✗
Practice › Codeforces Solutions › Codeforces Round 848 (Div. 2) ›

CF 1778E - The Tree Has Fallen!

We are given a tree with n nodes, where each node has an integer value written on it. Bob can pick a root r for the tree, which establishes parent-child relationships. Then Alice picks a node v, and Bob can choose any subset of nodes from the subtree rooted at v.
codeforces competitive-programming bitmasks dfs-and-similar math trees Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 848 (Div. 2) ›

CF 1778F - Maximizing Root

We are asked to maximize the value of the root of a tree after performing at most $k$ operations. Each operation allows us to pick a vertex $v$ that has not been selected before, choose a number $x$ that divides all values in $v$'s subtree, and multiply every value in that…
codeforces competitive-programming dfs-and-similar dp graphs math number-theory trees Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 848 (Div. 2) ›

CF 1778A - Flip Flop Sum

We are given an array consisting only of 1s and -1s. The task is to perform exactly one operation: select two consecutive elements and flip their signs. After doing this, we want to maximize the sum of all array elements.
codeforces competitive-programming greedy implementation Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 848 (Div. 2) ›

CF 1778D - Flexible String Revisit

Two binary strings of equal length evolve over time, but only one of them changes. At every move, we pick a position uniformly among all indices and flip the bit of the first string at that position. The second string is fixed.
codeforces competitive-programming combinatorics dp math probabilities Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 848 (Div. 2) ›

CF 1778B - The Forbidden Permutation

We are given a permutation p of the numbers 1...n. Another array a contains m distinct values that all appear in the permutation. For every value, we care only about its position inside the permutation. Let pos[x] be the index of value x in p.
codeforces competitive-programming greedy math Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 848 (Div. 2) ›

CF 1778C - Flexible String

We are given two equal-length strings, and we are allowed to modify the first string in a very specific way. Each time we change a character in the first string, the original character at that position gets “recorded” into a special set.
codeforces competitive-programming bitmasks brute-force strings Jun 9, 2026