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Sudoku Solver.cpp
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Sudoku Solver.cpp
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//Time Limit Exceeded, WHY????
//Finally find the reason!!!!!!!!!!!!!!!!!!
//isValidSudoku(vector<vector<char> > board,int dot) //如果board引用传递就不超时
//int findFirstDot(const vector<vector<char> > board) //不使用引用传递要重新复制一份两位数组,进而引起超时……
class Solution {
public:
bool isValidSudoku(vector<vector<char> > board,int dot) {
vector<bool> row(9,false);
vector<bool> col(9,false);
vector<bool> block(9,false);
int x = dot/9, y = dot%9;
for(int i=0;i<9;i++)
{
if(board[x][i]=='.') continue;
int index = board[x][i]-'1';
if(row[index]) return false;
row[index] = true;
}
for(int i=0;i<9;i++)
{
if(board[i][y]=='.') continue;
int index = board[i][y]-'1';
if(col[index]) return false;
col[index] = true;
}
for(int i=x/3*3;i<(x/3+1)*3;i++)
{
for(int j=y/3*3;j<(y/3+1)*3;j++)
{
if(board[i][j]=='.') continue;
int index = board[i][j]-'1';
if(block[index]) return false;
block[index] = true;
}
}
return true;
}
int findFirstDot(const vector<vector<char> > board)
{
for(int i=0;i<9;i++)
{
for(int j=0;j<9;j++)
{
if(board[i][j]=='.') return i*9+j;
}
}
return -1;
}
bool solveSudoku(vector<vector<char> > &board) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int dot = findFirstDot(board);
if(dot == -1) return true;
for(int i=1;i<=9;i++)
{
board[dot/9][dot%9]=i+'0';
if(isValidSudoku(board,dot) && solveSudoku(board)) return true;
board[dot/9][dot%9]='.';
}
return false;
}
};
//AC
class Solution {
public:
// 返回第一个空白的位置,如果没找到就返回 (-1, -1)
pair<int, int> findFirstEmpty(const vector< vector<char> >& board) {
for (int i = 0; i < 9; ++i)
for (int j = 0; j < 9; ++j)
if (board[i][j] == '.') return make_pair(i, j);
return make_pair(-1, -1);
}
// 检查连续的 9 个格子是否有效
bool isValid(const vector<char>& vec) {
vector<bool> occur(9, false);
for (int i = 0; i < 9; ++i) {
if (isdigit(vec[i])) {
if (occur[vec[i]-'1']) return false;
else occur[vec[i]-'1'] = true;
}
}
return true;
}
// 检查往某个位置填入一个数之后整个 board 是否有效(只需要考虑当前行、
// 当前列和所属的田字格)
bool isValidBoard(const vector< vector<char> >& board, pair<int, int> pos) {
// 检查当前行是否有效
if (!isValid(board[pos.first])) return false;
// 检查当前列是否有效
vector<char> column(9);
for (int i = 0; i < 9; ++i)
column[i] = board[i][pos.second];
if (!isValid(column)) return false;
// 检查所在的田字格是否有效
int block_row = pos.first / 3;
int block_col = pos.second / 3;
vector<char> block;
for (int i = block_row * 3; i < block_row * 3 + 3; ++i)
for (int j = block_col * 3; j < block_col * 3 + 3; ++j)
block.push_back(board[i][j]);
if (!isValid(block)) return false;
// 如果以上都有效,则返回 true
return true;
}
// 检查从当前局面开始是否能够得到最终合法有效的解
bool solveSudoku(vector<vector<char> >& board) {
// 如果没有找到空白的格子,说明已经填满了,成功返回
pair<int, int> pos = findFirstEmpty(board);
if (pos.first == -1 && pos.second == -1)
return true;
// 否则依次尝试往当前格子中填入数字 1-9,并判断能否得到可行的解
for (int i = 1; i <= 9; ++i) {
board[pos.first][pos.second] = i + '0';
if (isValidBoard(board, pos) && solveSudoku(board))
return true;
// 恢复原样
board[pos.first][pos.second] = '.';
}
return false;
}
};