CSES Subtree Queries

You are given a rooted tree consisting of n nodes. The nodes are numbered 1,2,…,n, and node 1 is the root. Each node has a value.

Your task is to process following types of queries:

1. change the value of node s to x

2. calculate the sum of values in the subtree of node s

Constraints

$1\le n, q \le 2 \cdot 10^5$
$1≤a,b,s≤n$

$1≤v_i,x≤10^9$

CSES Exponentiation II

Problem : Find the value of $(a^{b^c})mod(10^9+7)$ where $1\le n\le 10^5$ and $1\le a,b,c \le 10^9$

In order to solve this problem, we need to understand the Fermat's little theorem:

$(a^p\equiv a) mod(p)$ Where p is a prime number.

CSES Tree Matching

Tree Matching solved with dynamic programming

Let's define :

$dp(P,0)$ : The max matching number that DOES NOT INCLUDE node P.

$dp(P,1)$ : The max matching number that INCLUDES node P.