回溯 | #矩阵中的路径#

class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param matrix char字符型vector<vector<>>
     * @param word string字符串
     * @return bool布尔型
     */
    bool hasPath(vector<vector<char> >& matrix, string word) {
        int n = matrix.size(), m = matrix[0].size();
        vector<vector<bool> > visited(n, vector<bool>(m, false));
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (dfs(matrix, visited, n, m, i, j, word, 0))
                    return true;
            }
        }
        return false;
    }

    bool dfs(vector<vector<char> >& matrix, vector<vector<bool> >& visited, int n, int m, int i, int j, string word, int k) {
        if (i < 0 || i >= n || j < 0 || j >= m || 
            matrix[i][j] != word[k] || visited[i][j]) 
            return false;
        if (k == word.length() - 1) return true;
        visited[i][j] = true;
        if (dfs(matrix, visited, n, m, i + 1, j, word, k + 1) ||
            dfs(matrix, visited, n, m, i - 1, j, word, k + 1) ||
            dfs(matrix, visited, n, m, i, j + 1, word, k + 1) ||
            dfs(matrix, visited, n, m, i, j - 1, word, k + 1))
            return true;
        visited[i][j] = false;
        return false;
    }
};

C++ 初始化一个 2D vector<vector<bool>> visited （查询访问）的所有值为false：

vector<vector<bool>> visited( n, vector<bool>(m, false) );