leetcode/0079-word-search.py at master · rustykitty/leetcode · GitHub

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"""
79. Word Search

Submitted: March 30, 2026

Runtime: 973 ms (beats 93.20%)
Memory: 19.39 MB (beats 88.13%)
"""

from collections import Counter
from itertools import chain

class Solution:
    def exist(self, board: List[List[str]], word: str) -> bool:
        self.board = board
        self.n = len(board)
        self.m = len(board[0])

        # preprocess
        cb = Counter(chain.from_iterable(board))
        cw = Counter(word)
        for k in cw.keys():
            if cw[k] > cb[k]:
                return False

        del cb
        del cw

        self.word = word
        return any(
            self._exist(i, j, 0, set())
            for i in range(self.n)
            for j in range(self.m)
            if board[i][j] == word[0]
        )

    def _exist(self, i, j, pos, visited):
        word = self.word

        if pos >= len(word):
            return True
        if (i, j) in visited:
            return False
        elif i >= self.n or j >= self.m:
            return False
        elif i < 0 or j < 0:
            return False

        visited = visited | {(i, j)}

        if self.board[i][j] == word[pos]:
            return (
                self._exist(i - 1, j, pos + 1, visited) or
                self._exist(i, j - 1, pos + 1, visited) or
                self._exist(i + 1, j, pos + 1, visited) or
                self._exist(i, j + 1, pos + 1, visited)
            )
        return False