[Leetcode] Sudoku Solver

Sudoku Solver

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells is indicated by the character ‘.‘ .

Assume that there would be is only one unique solution.

A Sudoku Puzzle ...

... and its solution numbers marked in red.

Problem Solving Ideas:

I didn't play Sudoku before, so I went to the internet for a bit of evil. So I fell into a misunderstanding, sudoku several skills to use the program fully realized. So, tangled for a long time. It is very easy to use a programmer's mind, that is, backtracking. I realized that only a number of methods and ranks of the exclusion method, if not continue to solve, then use the law of violence. The code is as follows.

Class Solution {Public:void Solvesudoku (vector<vector<char> > &board) {set<int> allCan ({1, 2, 3, 4 , 5, 6, 7, 8, 9}); Map<int, set<int>> candidates;map<int, set<int>> rowleft;//What's left of a row map< int, set<int>> colleft;//which number is left in a column for (int i = 0; i < 9; i++) {rowleft[i] = allcan;colleft[i] = Allcan;} for (int i = 0; i<9; i++) {for (int j = 0; j<9; j + +) {if (board[i][j] = = '. ') {CANDIDATES[GET1D (I, j)] = allcan;prunning (board, I, J, candidates);} Else{rowleft[i].erase (board[i][j]-' 0 '); colleft[j].erase (Board[i][j]-' 0 ');}}} while (Candidates.size () >0) {int unknownumber = Candidates.size (); Showboard (board);//Only the remainder of the method {for (Map<int, set <int>>::iterator it = Candidates.begin (); It! = Candidates.end ();) {if (it->second.size () = = 1) {int i = Get2di (it->first); int j = GET2DJ (It->first); board[i ][J] = * (It->second.begin ()) + ' 0 '; Rowleft[i].erase (board[i][j]-' 0 '); colleft[j].erase (Board[i][j]-' 0 '); Candidates.erase (it++);}else{it++;}} for (int i = 0; i<9; i++) {for (int j = 0; j<9; j + +) {if (board[i][j] = = '. ') {prunning (board, I, J, candidates);}}} Line Exclusion method {for (int i = 0; i < 9; i++) {for (Set<int>::iterator it = Rowleft[i].begin (); It! = Rowleft[i].end ();) {int pos = -1;bool Onlyone = true;for (int j = 0; J < 9; J + +) {int index = GET1D (i, j); if (Candidates.find (index)! = Candidat Es.end () && candidates[index].find (*it)! = Candidates[index].end ()) {if (pos >= 0) {onlyone = False;break;} pos = j;}} if (onlyone&&pos >= 0) {Board[i][pos] = *it + ' 0 '; colleft[pos].erase (*it); Rowleft[i].erase (it++); Candidates.erase (GET1D (i, POS));} else{it++;}}} for (int i = 0, i < 9; i++) {for (int j = 0; J < 9; J + +) {if (board[i][j] = = '. ') {prunning (board, I, J, candidates);}}} Column Exclusion method {for (int j = 0; J < 9; J + +) {for (Set<int>::iterator it = Colleft[j].begin (); It! = Colleft[j].end ();) {int pos = -1;bool Onlyone = true;for (int i = 0; i < 9; i++) {int index = GET1D (i, j); if (candidates. Find (Index)! = Candidates.end () && candidates[index].find (*it)! = Candidates[index].end ()) {if (pos >= 0) { Onlyone = False;break;} pos = i;}} if (onlyone&&pos >= 0) {Board[pos][j] = *it + ' 0 '; rowleft[pos].erase (*it); Colleft[j].erase (it++); Candidates.erase (GET1D (POS, J));} else{it++;}}} for (int i = 0; i<9; i++) {for (int j = 0; j<9; j + +) {if (board[i][j] = = '. ') {prunning (board, I, J, candidates);}}} if (Unknownumber = = Candidates.size ()) {break;}} If still not answered, then violent enumeration if (Candidates.size () > 0) {dfscheck (board, candidates, Candidates.begin ());} Showboard (board);} BOOL Dfscheck (vector<vector<char> > &board, Map<int, set<int>> &candidates, map< int, set<int>>::iterator it) {if (it = = Candidates.end ()) {return true;} int i = Get2di (it->first); int j = GET2DJ (It->first); for (Set<int>::iterator Setit = It->second.begin (); SE Tit! = It->second.end (); setit++) {Board[i][j] = *setit+ ' 0 '; it++;if (Isvalidsudoku (board) &&Dfscheck (Board, candidates, it)) {return true;} IT--;BOARD[I][J] = '. ';}} Private:int get1d (int i, int j) {return I * 9 + j;} int get2di (int index) {return INDEX/9;} int get2dj (int index) {return index% 9;} void Showboard (Vector<vector<char> > &board) {/*for (int i = 0; i < 9; i++) {for (int j = 0; J < 9; j+ +) {cout << board[i][j];if ((j + 1)% 3 = = 0) {cout << "";}} cout << Endl;} cout << endl;*/};void prunning (vector<vector<char> > &board, int i, Int J, Map<int, SET&LT;INT&G T;> &candidates) {pruninggrid (board, I, J, candidates);p Runingrow (board, I, J, candidates);p Runingcolumn (board, I, J, candidates);} void Pruninggrid (Vector<vector<char> > &board, int i, Int J, Map<int, Set<int>> & Candidates) {int index = GET1D (i, j); while (i% 3! = 0) {i--;} while (j% 3! = 0) {j--;} for (int m = i, M < i + 3; m++) {for (int n = j; n < j + 3; n++) {if (board[m][n]! = '. ') {candidates[index].erase (Board[m][n]- ' 0 ');}}} void Pruningrow (Vector<vector<char> > &board, int i, Int J, Map<int, Set<int>> & Candidates) {int index = GET1D (i, j); for (int m = 0; m < 9; m++) {if (board[i][m]! = '. ') {candidates[index].erase (board[i][m]-' 0 ');}}} void Pruningcolumn (Vector<vector<char> > &board, int i, Int J, Map<int, Set<int>> & Candidates) {int index = GET1D (i, j); for (int m = 0; m < 9; m++) {if (board[m][j]! = '. ') {candidates[index].erase (board[m][j]-' 0 ');}}} BOOL Isvalidsudoku (vector<vector<char>>& board) {//verifies that each row is valid for (int i = 0; i<9; i++) {if (! Checkrowvalid (Board, I)) {return false;}} Verify that each column is valid for (int i = 0; i<9; i++) {if (!checkcolumnvalid (board, I)) {return false;}} Verify that each of the cells is valid for (int i = 0; i<9; i = i + 3) {for (int j = 0; j<9; j = j + 3) {if (!checkgridvalid (board, I, J)) {return false;}}} return true;} Verifies that each lattice is valid, passing in the upper-left corner of the subscript bool Checkgridvalid (vector<vector<char>>& board, int m, int n) {bool FLag[9];memset (flag, 0, sizeof (BOOL) * 9), for (int i = m; i<m + 3; i++) {for (int j = n; j<n + 3; j + +) {if (Board[i][j] == '.') {continue;} if (Flag[board[i][j]-' 1 ']) {return false;} FLAG[BOARD[I][J]-' 1 '] = true;}} return true;} Verify that each row is valid, passing in the line number bool Checkrowvalid (vector<vector<char>>& board, int m) {bool Flag[9];memset (flag, 0 , sizeof (BOOL) * 9), for (int i = 0; i<9; i++) {if (board[m][i] = = '. ') {continue;} if (Flag[board[m][i]-' 1 ']) {return false;} Flag[board[m][i]-' 1 '] = true;} return true;} Verify that each column is valid, passing in the column number bool Checkcolumnvalid (vector<vector<char>>& board, int n) {bool Flag[9];memset ( Flag, 0, sizeof (BOOL) * 9); for (int i = 0; i<9; i++) {if (board[i][n] = = '. ') {continue;} if (Flag[board[i][n]-' 1 ']) {return false;} Flag[board[i][n]-' 1 '] = true;} return true;}};

[Leetcode] Sudoku Solver