Today I have done leetcode's November LeetCoding Challenge with cpp.

November LeetCoding Challenge 5

Description

Word Search II

Given an m x n board of characters and a list of strings words, return all words on the board.

Each word must be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word.

Example 1:

Input: board = [["o","a","a","n"],["e","t","a","e"],["i","h","k","r"],["i","f","l","v"]], words = ["oath","pea","eat","rain"]
Output: ["eat","oath"]

Example 2:

Input: board = [["a","b"],["c","d"]], words = ["abcb"]
Output: []

Constraints:

• m == board.length
• n == board[i].length
• 1 <= m, n <= 12
• board[i][j] is a lowercase English letter.
• 1 <= words.length <= 3 * 104
• 1 <= words[i].length <= 10
• words[i] consists of lowercase English letters.
• All the strings of words are unique.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
struct TrieNode {
  bool end = false;
  int count = 0;
  TrieNode *child[26] = {};
};
void insert(TrieNode *root, const string &word) {
  TrieNode *cur = root;
  for(auto c : word) {
    c = c - 'a';
    if(!cur->child[c]) {
      cur->child[c] = new TrieNode();
    }
    cur = cur->child[c];
    cur->count += 1;
  }
  cur->end = true;
}
int prune(TrieNode *root, const string &word) {
  TrieNode *cur = root;
  int backStep = word.length();
  // cout << word << endl;
  for(auto c : word) {
    // cout << c ;
    c = c - 'a';
    // cout << cur->child[c]->count;
    if(cur->child[c]->count == 1) {
      // delete then RE, fuck u leetcode
      cur->child[c] = nullptr;
      break;
    } else {
      backStep -= 1;
      cur = cur->child[c];
      cur->count -= 1;
    }
  }
  if(!backStep) cur->end = false;
  // cout << endl << backStep << endl;
  return backStep;
}
constexpr int moves[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
class Solution {
  vector<vector<bool>> vis;
  vector<string> words;
  string current;
  int rows;
  int cols;
  TrieNode *root = new TrieNode();
  void solve(const vector<vector<char>>& board, TrieNode *currentNode, int row, int col, int &backStep) {
    currentNode = currentNode->child[board[row][col] - 'a'];
    vis[row][col] = true;
    current.push_back(board[row][col]);
    if(currentNode) {
      if(currentNode->end) {
        words.push_back(current);
        backStep = prune(root, current);
      }
      for(int i = 0; !backStep && i < 4; ++i) {
        int newRow = row + moves[i][0];
        int newCol = col + moves[i][1];
        if(newRow < 0 || newCol < 0 || newRow >= rows || newCol >= cols) continue;
        if(vis[newRow][newCol]) continue;
        solve(board, currentNode, newRow, newCol, backStep);
      }
    }
    if(backStep) {
      backStep -= 1;
    }
    vis[row][col] = false;
    current.pop_back();
  }
public:
  vector<string> findWords(vector<vector<char>>& board, vector<string>& w) {
    rows = board.size();
    cols = board.front().size();
    vis.resize(rows, vector<bool>(cols));
    for(auto &word : w) {
      insert(root, word);
    }
    int backStep = 0;
    for(int i = 0; i < rows; ++i) {
      for(int j = 0; j < cols; ++j) {
        solve(board, root, i, j, backStep);
      }
    }
    return words;
  }
};

// Accepted
// 64/64 cases passed (227 ms)
// Your runtime beats 95.83 % of cpp submissions
// Your memory usage beats 35.69 % of cpp submissions (15.3 MB)