LeetCode第37之Sudoku Solver

主要思路：回溯法，每个‘.’的位置遍历“1-9”，如果满足则继续下一个位置，如果遍历完“1-9”仍不满足则将该位置改为‘.’,然后回溯到上一个位置。
缺点就是运行时间有点长。
C++代码：

#include <iostream>#include <vector>using namespace std;//打印board矩阵void print_vec(vector<vector<char>> &board){    for (vector<vector<char>>::iterator ita=board.begin();ita!=board.end();++ita)    {        for (vector<char>::iterator itb=ita->begin();itb!=ita->end();++itb)        {            cout<<*itb;        }        cout<<endl;    }    cout<<endl;}class Solution {private:    //falg指示是否找到解    bool falg;public:    //检查如果（i, j）的位置放数字n，第i行、第j列，以及（i,j）所在的块是否产生冲突    bool isValid(vector<vector<char>> &board, int i, int j, int n)    {        vector<bool> appear;        //检查第i行是否满足        appear.assign(9, false);        //appear[n-1] = true;        for (int k=0;k<9;++k)        {            if (board[i][k] != '.')            {                int num = board[i][k]-'0';                if (appear[num-1])                    return false;                appear[num-1] = true;            }        }        //检查第j列是否满足        appear.assign(9, false);        //appear[n-1] = true;        for (int k=0;k<9;++k)        {            if (board[k][j] != '.')            {                int num = board[k][j]-'0';                if (appear[num-1])                    return false;                appear[num-1] = true;            }        }        //检查（i, j）所在的块是否满足        appear.assign(9, false);        int x = i-i%3;        int y = j-j%3;        for (int m=x;m<x+3;++m)        {            for (int n=y;n<y+3;++n)            {                if (board[m][n] != '.')                {                    int num = board[m][n]-'0';                    if (appear[num-1])                        return false;                    appear[num-1] = true;                }            }        }        return true;    }    //给(i，j)的位置赋值    void fun_try(vector<vector<char>> &board, int i, int j)    {    //  print_vec(board);        if (board[i][j] == '.')        {            for (int n=1;n<10;++n)            {                board[i][j] = n+'0';                if (isValid(board, i, j, n))                {                    if (i == board.size()-1 && j == board.size()-1)                    {        //              print_vec(board);                        //答案已经找到                        falg =true;                        return;                    }                    if (j == board.size()-1)                    {                        fun_try(board, i+1, 0);                    }                    else                    {            //          print_vec(board);                        fun_try(board, i, j+1);                    }                    //如果答案已经找到则返回                    if (falg)                    {                        return;                    }                }            }            //回溯            board[i][j] = '.';        }        else        {            if (isValid(board, i, j, board[i][j]-'0'))            {                if (i == board.size()-1 && j == board.size()-1)                {            //      print_vec(board);                    //答案已经找到                    falg =true;                    return;                }                if (j == board.size()-1)                {                    fun_try(board, i+1, 0);                }                else                {                    fun_try(board, i, j+1);                }                //如果答案已经找到则返回                if (falg)                {                    return;                }            }        }    }    void solveSudoku(vector<vector<char>>& board) {        falg = false;        fun_try(board, 0, 0);    }};int main(){    Solution s;    vector<vector<char>> board;    vector<char> board0;    board0.assign(9,'.');    board0[0]='5';    board0[1]='3';    board0[4]='7';    board.push_back(board0);    board0.assign(9,'.');    board0[0]='6';    board0[3]='1';    board0[4]='9';    board0[5]='5';    board.push_back(board0);    board0.assign(9,'.');    board0[1]='9';    board0[2]='8';    board0[7]='6';    board.push_back(board0);    board0.assign(9,'.');    board0[0]='8';    board0[4]='6';    board0[8]='3';    board.push_back(board0);    board0.assign(9,'.');    board0[0]='4';    board0[3]='8';    board0[5]='3';    board0[8]='1';    board.push_back(board0);    board0.assign(9,'.');    board0[0]='7';    board0[4]='2';    board0[8]='6';    board.push_back(board0);    board0.assign(9,'.');    board0[1]='6';    board0[6]='2';    board0[7]='8';    board.push_back(board0);    board0.assign(9,'.');    board0[3]='4';    board0[4]='1';    board0[5]='9';    board0[8]='5';    board.push_back(board0);    board0.assign(9,'.');    board0[4]='8';    board0[7]='7';    board0[8]='9';    board.push_back(board0);    print_vec(board);    s.solveSudoku(board);    print_vec(board);    return 0;}