[itint5]单词游戏

http://www.itint5.com/oj/#36

此题在数据大些，而且全是A的情况下会超时（因为要匹配到很后面才false）。通过利用数组本身作为visited标示，而且使用string引用，得意通过。

bool find(vector<vector<char> > &grid, string &pattern, int i, int j, int k) {
    if (k == pattern.length()) return true;
    int m = grid.size();
    int n = grid[0].size();
    if (i < 0 || i >= m || j < 0 || j >= n) return false;
    if (pattern[k] == grid[i][j] && grid[i][j] != '#') {
        char c = grid[i][j];
        grid[i][j] = '#';
        if (find(grid, pattern, i-1, j, k+1) ||
            find(grid, pattern, i+1, j, k+1) || 
            find(grid, pattern, i, j-1, k+1) || 
            find(grid, pattern, i, j+1, k+1)) {
            grid[i][j] = c;
            return true;
        } else {
            grid[i][j] = c;
            return false;
        }
    } else {
        return false;
    }
}

bool exists(vector<vector<char> > &grid, string pattern) {
    int m = grid.size();
    if (m == 0) return false;
    int n = grid[0].size();
    if (n == 0) return false;
    for (int i = 0; i < m; i++) {
        for (int j = 0; j < n; j++) {
            if (find(grid, pattern, i, j, 0)) return true;
        }
    }
    return false;
}