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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0001_0100.s0079_word_search;

// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Matrix #Backtracking
// #Algorithm_II_Day_11_Recursion_Backtracking #Big_O_Time_O(4^(m*n))_Space_O(m*n)
// #2024_11_11_Time_64_ms_(98.51%)_Space_41.6_MB_(51.63%)

public class Solution {
    private boolean exists = false;

    public boolean exist(char[][] board, String word) {
        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[0].length; j++) {
                if (board[i][j] == word.charAt(0)) {
                    dfs(board, word, 1, i, j);
                }
            }
        }
        return exists;
    }

    private void dfs(char[][] board, String word, int wordIndex, int i, int j) {
        if (wordIndex == word.length()) {
            exists = true;
            return;
        }
        char currentChar = board[i][j];
        char nextChar = word.charAt(wordIndex);
        if (i > 0 && board[i - 1][j] == nextChar) {
            // go up
            board[i][j] = '-';
            dfs(board, word, wordIndex + 1, i - 1, j);
            board[i][j] = currentChar;
        }
        if (j > 0 && board[i][j - 1] == nextChar) {
            // go left
            board[i][j] = '-';
            dfs(board, word, wordIndex + 1, i, j - 1);
            board[i][j] = currentChar;
        }
        if (i < board.length - 1 && board[i + 1][j] == nextChar) {
            // go down
            board[i][j] = '-';
            dfs(board, word, wordIndex + 1, i + 1, j);
            board[i][j] = currentChar;
        }
        if (j < board[0].length - 1 && board[i][j + 1] == nextChar) {
            // go right
            board[i][j] = '-';
            dfs(board, word, wordIndex + 1, i, j + 1);
            board[i][j] = currentChar;
        }
    }
}