37.数独求解
Sudoku Solver
问题描述：
Write a program to solve a Sudoku puzzle by filling the empty cells.
Empty cells are indicated by the character ‘.’.
You may assume that there will be only one unique solution.
A sudoku puzzle…
…and its solution numbers marked in red.
知识补充：
学会灵活使用结构体，结构体也可以作为元素放入栈和队列中。这样的话就有多种存储数据的方法了
char型相互转化为int型
char c = '1';
int i;
i = (int)c;//强制转换
i = c-'0';//差值即为所要转换数字
c = (char)i;//强制转换
c = char(48+i);//通过差值转换参考答案：
class Solution {
bool check(vector<vector<char>> &board, int i, int j, char val)
{
int row = i - i%3, column = j - j%3;
for(int x=0; x<9; x++) if(board[x][j] == val) return false;
for(int y=0; y<9; y++) if(board[i][y] == val) return false;
for(int x=0; x<3; x++)
for(int y=0; y<3; y++)
if(board[row+x][column+y] == val) return false;
return true;
}
bool solveSudoku(vector<vector<char>> &board, int i, int j)
{
if(i==9) return true;
if(j==9) return solveSudoku(board, i+1, 0);
if(board[i][j] != '.') return solveSudoku(board, i, j+1);
for(char c='1'; c<='9'; c++)
{
if(check(board, i, j, c))
{
board[i][j] = c;
if(solveSudoku(board, i, j+1)) return true;
board[i][j] = '.';
}
}
return false;
}
public:
void solveSudoku(vector<vector<char>>& board) {
solveSudoku(board, 0, 0);
}
};性能：
参考答案：
class ValidMoves {
private:
int num_valid;
int blocked_count[9];
public:
ValidMoves()
: num_valid(9), blocked_count {0, 0, 0, 0, 0, 0, 0, 0, 0}
{}
inline int valid() const { return num_valid; }
inline void block(int move) {
mod(move, 1);
}
inline void unblock(int move) {
mod(move, -1);
}
void mod(int move, int d) {
if(blocked_count[move] == 0) {
num_valid--;
}
blocked_count[move] += d;
if(blocked_count[move] == 0) {
num_valid++;
}
}
inline bool isValid(int move) const { return blocked_count[move] == 0; }
};
class Solution {
public:
void solveSudoku(vector<vector<char>>& board) {
vector<vector