[leetcode 37]sudoku solver

1 题目：

根据给出的数独，全部填出来

2 思路：

为了做出来，我自己人工做了一遍题目给的数独。思路是看要填的数字横、竖、子是否已经有1-9的数字，有就剔除一个，最后剩下一个的话，就填上。一遍一遍的循环，直到填完为止。

后来发现，这个思路只能解决部分数独。还有部分数独是需要回溯的，比如，这个位置只能填3或5，那么就需要先填上3，看看能否继续填下去，不能的话，再回过来填5。

想了半天，想不出来，把别人的backtracking看懂了，写出来了。。

3 代码：

自己的：

Hashtable<Integer, List<Character>> table;
int row;
int column;
int totalNum;

public void solveSudoku(char[][] board) {
if (board.length == 0) {
return;
}

row = board.length;
column = board[0].length;
totalNum = row * column;
table = new Hashtable<Integer, List<Character>>(totalNum);
for (int i = 0; i < row; i++) {
for (int j = 0; j < column; j++) {
if (board[i][j] == '.') {
List<Character> validNum = new ArrayList<Character>();
Character[] nums = {'1','2','3','4','5','6','7','8','9'};
validNum.addAll(Arrays.asList(nums));
table.put(i*row+j, validNum);
}else {

}
}
}

fillBoard(board);
}

private void fillBoard(char[][] board)
{
for (int i = 0; i < row; i++) {
System.out.println();
for (int j = 0; j < column; j++) {
int index = i*column + j;
if (table.containsKey(index)) {
// 判断剩余的数字
calRemaingNum(i,j,index,board);
}

}
}
System.out.println("++++++++++++++++++++++++++++++++++++++");
if (isSuccess()) {
return;
}
fillBoard(board);
}

private void calRemaingNum(int i, int j, int calIndex,char[][] board)
{
//row
for(int k=0; k< column; k++){
if (board[i][k] != '.') {
table.get(calIndex).remove((Character)board[i][k]);
}
}

//column
for (int k = 0; k < row; k++) {
if (board[k][j] != '.') {
table.get(calIndex).remove((Character)board[k][j]);
}
}

//square
int m = i / 3;
int n = j / 3;
for (int k = 0; k < 3; k++) {
for (int k2 = 0; k2 < 3; k2++) {
if (board[m*3+k][n*3+k2] != '.') {
table.get(calIndex).remove((Character)board[m*3+k][n*3+k2]);
}
}
}
System.out.println("i=" + i + " , j = " + j +  ",index = " + calIndex + "  ++ " + table.get(calIndex));
if (table.get(calIndex).size() == 1) {
board[i][j] = table.get(calIndex).get(0);
table.remove(calIndex);
}
}

private boolean isSuccess(){
return table.size() == 0;
}

别人的

public void solveSudoku(char[][] board) {
if (board==null || board.length == 0) {
return;
}

fillboard(board);
}

private boolean fillboard(char[][] board){
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[0].length; j++) {
if(board[i][j] == '.'){
for(char ch = '1'; ch <= '9'; ch++){
if (isValid(i, j, ch, board)) {
System.out.println("ok, i = " + i + ", j = " + j + " ,  value = " + ch);
board[i][j] = ch;

if (fillboard(board)) {
return true;
}else {
board[i][j] = '.';
}
}
}
return false;
}
}
}

return true;
}

private boolean isValid(int row, int column, char value, char[][] board){
// row
for (int i = 0; i < board.length; i++) {
if (board[row][i] == value) {
return false;
}
}

// column
for (int i = 0; i < board[0].length; i++) {
if (board[i][column] == value) {
return false;
}
}

// square
int m = row / 3;
int n = column / 3;
for (int k = 0; k < 3; k++) {
for (int k2 = 0; k2 < 3; k2++) {
if (board[m*3+k][n*3+k2] == value) {
return false;
}
}
}
return true;
}