44
55using namespace std ;
66
7- class Solution {
7+ // 108 ms
8+ class Solution0 {
89public:
910 struct Trace {
1011 int i;
@@ -82,7 +83,7 @@ class Solution {
8283 }
8384 // can't find a right number, backtrack
8485 // set back the flag to false
85- // be aware to set the previout number, not the current
86+ // be aware to set the previous number, not the current
8687 if (count <= 0 ) return ;
8788 Trace t = ans[count - 1 ];
8889 rowFlag[t.i ][t.s ] = false ;
@@ -96,6 +97,71 @@ class Solution {
9697 }
9798};
9899
100+ // 36 ms
101+ class Solution {
102+ public:
103+ void solveSudoku (vector<vector<char >>& board) {
104+ vector<vector<bool >> rowFlag (10 , vector<bool >(10 , false ));
105+ vector<vector<bool >> colFlag (10 , vector<bool >(10 , false ));
106+ vector<vector<bool >> boxFlag (10 , vector<bool >(10 , false ));
107+ int i, j;
108+ for (i = 0 ; i < 9 ; i++) {
109+ for (j = 0 ; j < 9 ; j++) {
110+ if (board[i][j] != ' .'
111+ int k = board[i][j] - ' 1'
112+ rowFlag[i][k] = true ;
113+ colFlag[j][k] = true ;
114+ boxFlag[(i / 3 ) * 3 + j / 3 ][k] = true ;
115+ }
116+ }
117+ }
118+ 119+ bool found = false ;
120+ placeNumber (board, found, 0 , rowFlag, colFlag, boxFlag);
121+ }
122+ 123+ bool placeNumber (vector<vector<char >>& board, bool &found,
124+ int depth,
125+ vector<vector<bool >> &rowFlag,
126+ vector<vector<bool >> &colFlag, vector<vector<bool >> &boxFlag)
127+ {
128+ // suppose we have only one solution, if we found one, no need to continue
129+ if (found) return true ;
130+ 131+ // found one solution! copy answers to the board
132+ if (depth == 81 ) {
133+ found = true ;
134+ return true ;
135+ }
136+ 137+ int i, j;
138+ i = depth / 9 ; j = depth % 9 ;
139+ 140+ if (board[i][j] != ' .'
141+ return placeNumber (board, found, depth + 1 , rowFlag, colFlag, boxFlag);
142+ }
143+ else {
144+ for (int s = 0 ; s < 9 ; s++) {
145+ // if it's valid, set flag and place another number
146+ if (!rowFlag[i][s] && !colFlag[j][s] && !boxFlag[(i / 3 ) * 3 + j / 3 ][s]) {
147+ // try to place a number
148+ board[i][j] = s + ' 1'
149+ rowFlag[i][s] = true ;
150+ colFlag[j][s] = true ;
151+ boxFlag[(i / 3 ) * 3 + j / 3 ][s] = true ;
152+ if (placeNumber (board, found, depth + 1 , rowFlag, colFlag, boxFlag)) return true ;
153+ // backtrack
154+ rowFlag[i][s] = false ;
155+ colFlag[j][s] = false ;
156+ boxFlag[(i / 3 ) * 3 + j / 3 ][s] = false ;
157+ board[i][j] = ' .'
158+ }
159+ }
160+ return false ;
161+ }
162+ }
163+ };
164+ 99165int main () {
100166 vector<string> board0 = {
101167 " ..9748..."
0 commit comments