This is a C++ code that defines a struct Matrix...

March 30, 2023 at 06:33 PM

#include<bits/stdc++.h>
using namespace std;
const int inf = 42e6;

#define FOR(i) for(int i = 0; i < 3; ++i)
#define mini(a,b) a = min(a, b)

struct Matrix {

	int t[3][3][3];
	Matrix(int fill) {
		FOR(a)FOR(b)FOR(c) t[a][b][c] = fill;
	}
	Matrix operator * (Matrix m2) {
		Matrix res(inf);
		FOR(needNow1)FOR(a1)FOR(needUp1) {
			int x = t[needNow1][a1][needUp1];
			FOR(needNow2)FOR(a2)FOR(needUp2) {
				int y = m2.t[needNow2][a2][needUp2];
				int needNow = max(needNow1, needNow2);
				int a = min(2, a1 + a2);
				int needUp = max(0, max(needUp1-a2, needUp2-a1));
				mini(res.t[needNow][a][needUp], x + y);
			}
		}
		return res;
	}
};

const int nax = 1e6 + 5;
vector<int> w[nax];

Matrix dfs(int a, int par) {
	Matrix me(-4);
	bool nil = true;
	for(int i = 0; i < (int) w[a].size(); ++i) {
		int b = w[a][i];
		if(b != par) {
			if(nil) {
				me = dfs(b, a);
				nil = false;
			}
			else me = dfs(b, a) * me;
		}
	}

This is a C++ code that defines a struct Matrix and a function dfs. The Matrix struct represents a 3D matrix of dimensions 3x3x3, with each element initialized to a given integer value. It also overloads the * operator to perform matrix multiplication.

The dfs function takes two integer parameters, a and par, and returns a Matrix object. It performs a depth-first search on a tree represented by a graph stored in a vector of vectors w. Starting at node a, it recursively traverses the tree, multiplying the matrices returned by its children using the overloaded * operator and stores the result in the me variable. The purpose of this function is not clear from the given code snippet without additional context.

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