【leetcode】Valid Sudoku

问题：

bool isValidSudoku(vector<vector<char> > &board) {

const int M = 9;//9 * 9
const int hash_len = 60;//'0' = 48 + 10
const char dot = '.';
//check rows
for(int i = 0; i < M; ++i)
{
bool rows[hash_len] = {false};
bool cols[hash_len] = {false};
for(int j = 0; j < M; ++j){
if(board[i][j] != dot)
{
if(rows[board[i][j]])
return false;
else
rows[board[i][j]] = true;
}

}
}
//check cols
for(int i = 0; i < M; ++i)
{
bool rows[hash_len] = {false};
for(int j = 0; j < M; ++j){
if(board[j][i] != dot)
{
if(rows[board[j][i]])
return false;
else
rows[board[j][i]] = true;
}
}
}
//check inner boxes. 9 * (3 * 3)
const int N = 3;
for(int ibox = 0; ibox < M; ++ibox)
{
bool box[hash_len] = {false};
for (int irow = 0; irow < N; ++irow)
{
for (int icol = 0; icol < N; ++icol)
{
if(board[ibox/N*N + irow][ibox%N*N + icol] != dot &&
box[board[ibox/N*N + irow][ibox%N*N + icol]])
return false;
if(board[ibox/N*N + irow][ibox%N*N + icol] != dot)
box[board[ibox/N*N + irow][ibox%N*N + icol]] = true;
}
}
}
return true;
}