Boggle board solver in C++

boggle_board.cc

#include <bits/stdc++.h>
using namespace std;

struct Node {
	vector<int> endings;
	unordered_map<char, Node*> followers;
};

void insert_trie(Node *node, const string &word, int index) {
	int ws = word.size();
	for(int i = 0; i < ws; i++) {
		if(node->followers.find(word[i]) == node->followers.end()) node->followers[word[i]] = new Node;
		node = node->followers[word[i]];
	}
	node->endings.push_back(index);
}

bool is_in(const int i, const int j, const int height, const int width) {
	return 0 <= i && i < height && 0 <= j && j < width;
}

const vector<pair<int, int>> deltas {
	{0, 1},
	{0, -1},
	{1, 0}, 
	{-1, 0},
	{1, 1},
	{-1, -1},
	{1, -1},
	{-1, 1}
};

void fill_in(const vector<vector<char>> &board, const int i, const int j, Node *node, vector<bool> &was, vector<vector<bool>> &occupied) {
	const int height = board.size(), width = board[0].size();
	if(is_in(i, j, height, width) && !occupied[i][j] && node->followers.find(board[i][j]) != node->followers.end()) {
		occupied[i][j] = true;
		Node *new_node = node->followers[board[i][j]];
		for(const auto index : new_node->endings) was[index] = true;
		for(const auto &delta : deltas) fill_in(board, i + delta.first, j + delta.second, new_node, was, occupied);
		occupied[i][j] = false;
	}
}

vector<string> boggleBoard(vector<vector<char>> board, vector<string> words) {
	int ws = words.size();
	vector<bool> was(ws, false);
	int height = board.size(), width = board[0].size();
	vector<vector<bool>> occupied(height, vector<bool>(width, false));
	Node *root = new Node;
	for(int i = 0; i < ws; i++) insert_trie(root, words[i], i);
	for(int i = 0; i < height; i++) {
		for(int j = 0; j < width; j++) {
			fill_in(board, i, j, root, was, occupied);
		}
	}
	vector<string> ret;
	for(int i = 0; i < ws; i++) {
		if(was[i]) ret.push_back(words[i]);
	}
	return ret;
}