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163 lines (146 loc) · 6.79 KB
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package Sudoku;
public final class SudokuSolver {
public static void main(String[] args) {
SudokuSolver ss = new SudokuSolver();
System.out.println(ss.run());
}
private int[][] board = new int[9][9];
public String run(){
int sum = 0;
for(String p : BOARDS){
Sudoku puzz = new Sudoku(p);
if (!puzz.solve()){
throw new AssertionError();
}
sum += 100*board[0][0] + 10*board[0][1] + board[0][2];
}
return Integer.toString(sum);
}
public class Sudoku{
public boolean[][] usedInRow = new boolean[9][9];
public boolean[][] usedInCol = new boolean[9][9];
public boolean[][][] usedInBox = new boolean[3][3][9];
public Sudoku(String puzzle){
int i;
if(puzzle.length()!=81){
throw new IllegalArgumentException("Invalid length");
}
for(i=0;i<81;i++){
board[i/9][i%9] = (int)(puzzle.charAt(i) - '0');
}
}
public boolean solve(){
for(int y=0;y<9;y++){
for(int x=0;x<9;x++){
if(board[y][x] == 0){
continue;
}
int val = board[y][x] - 1;
usedInRow[y][val] = true;
usedInCol[x][val] = true;
usedInBox[y/3][x/3][val] = true;
}
}
return solve(0) && isValid();
}
private boolean solve(int index){
while(index < 81 && board[index/9][index%9] != 0){
index++;
}
if(index == 81){
return true;
}
// First zero(empty) box
int y = index/9;
int x = index%9;
for(int val=0;val<9;val++){
if(!usedInRow[y][val] && !usedInCol[x][val] && !usedInBox[y/3][x/3][val]){ // Placing constraints
board[y][x] = val+1;
usedInRow[y][val] = true;
usedInCol[x][val] = true;
usedInBox[y/3][x/3][val] = true;
if(solve(index+1)){ // Checking if it is indeed the value in the box, or just a false positive from a potential candidate
return true;
}
usedInRow[y][val] = false;
usedInCol[x][val] = false;
usedInBox[y/3][x/3][val] = false;
}
}
board[y][x] = 0;
return false;
}
private boolean isValid(){
boolean rowUsed[][] = new boolean[9][9];
boolean colUsed[][] = new boolean[9][9];
boolean boxUsed[][][] = new boolean[3][3][9];
for(int y=0;y<9;y++){
for(int x=0;x<9;x++){
if(board[y][x] == 0){
continue;
}
int val = board[y][x] - 1;
if(rowUsed[y][val] || colUsed[x][val] || boxUsed[y/3][x/3][val]){
return false;
}
rowUsed[y][val] = true;
colUsed[x][val] = true;
boxUsed[y/3][x/3][val] = true;
}
}
return true;
}
}
public String[] BOARDS = {
"003020600900305001001806400008102900700000008006708200002609500800203009005010300",
"200080300060070084030500209000105408000000000402706000301007040720040060004010003",
"000000907000420180000705026100904000050000040000507009920108000034059000507000000",
"030050040008010500460000012070502080000603000040109030250000098001020600080060020",
"020810740700003100090002805009040087400208003160030200302700060005600008076051090",
"100920000524010000000000070050008102000000000402700090060000000000030945000071006",
"043080250600000000000001094900004070000608000010200003820500000000000005034090710",
"480006902002008001900370060840010200003704100001060049020085007700900600609200018",
"000900002050123400030000160908000000070000090000000205091000050007439020400007000",
"001900003900700160030005007050000009004302600200000070600100030042007006500006800",
"000125400008400000420800000030000095060902010510000060000003049000007200001298000",
"062340750100005600570000040000094800400000006005830000030000091006400007059083260",
"300000000005009000200504000020000700160000058704310600000890100000067080000005437",
"630000000000500008005674000000020000003401020000000345000007004080300902947100080",
"000020040008035000000070602031046970200000000000501203049000730000000010800004000",
"361025900080960010400000057008000471000603000259000800740000005020018060005470329",
"050807020600010090702540006070020301504000908103080070900076205060090003080103040",
"080005000000003457000070809060400903007010500408007020901020000842300000000100080",
"003502900000040000106000305900251008070408030800763001308000104000020000005104800",
"000000000009805100051907420290401065000000000140508093026709580005103600000000000",
"020030090000907000900208005004806500607000208003102900800605007000309000030020050",
"005000006070009020000500107804150000000803000000092805907006000030400010200000600",
"040000050001943600009000300600050002103000506800020007005000200002436700030000040",
"004000000000030002390700080400009001209801307600200008010008053900040000000000800",
"360020089000361000000000000803000602400603007607000108000000000000418000970030014",
"500400060009000800640020000000001008208000501700500000000090084003000600060003002",
"007256400400000005010030060000508000008060200000107000030070090200000004006312700",
"000000000079050180800000007007306800450708096003502700700000005016030420000000000",
"030000080009000500007509200700105008020090030900402001004207100002000800070000090",
"200170603050000100000006079000040700000801000009050000310400000005000060906037002",
"000000080800701040040020030374000900000030000005000321010060050050802006080000000",
"000000085000210009960080100500800016000000000890006007009070052300054000480000000",
"608070502050608070002000300500090006040302050800050003005000200010704090409060701",
"050010040107000602000905000208030501040070020901080406000401000304000709020060010",
"053000790009753400100000002090080010000907000080030070500000003007641200061000940",
"006080300049070250000405000600317004007000800100826009000702000075040190003090600",
"005080700700204005320000084060105040008000500070803010450000091600508007003010600",
"000900800128006400070800060800430007500000009600079008090004010003600284001007000",
"000080000270000054095000810009806400020403060006905100017000620460000038000090000",
"000602000400050001085010620038206710000000000019407350026040530900020007000809000",
"000900002050123400030000160908000000070000090000000205091000050007439020400007000",
"380000000000400785009020300060090000800302009000040070001070500495006000000000092",
"000158000002060800030000040027030510000000000046080790050000080004070100000325000",
"010500200900001000002008030500030007008000500600080004040100700000700006003004050",
"080000040000469000400000007005904600070608030008502100900000005000781000060000010",
"904200007010000000000706500000800090020904060040002000001607000000000030300005702",
"000700800006000031040002000024070000010030080000060290000800070860000500002006000",
"001007090590080001030000080000005800050060020004100000080000030100020079020700400",
"000003017015009008060000000100007000009000200000500004000000020500600340340200000",
"300200000000107000706030500070009080900020004010800050009040301000702000000008006",
};
}