# Less than 30 line clean java solution using DFS

• Should be very easy to understand.

``````public class Solution {
public void solveSudoku(char[][] board) {
dfs(board,0);
}
private boolean dfs(char[][] board, int d) {
if (d==81) return true; //found solution
int i=d/9, j=d%9;
if (board[i][j]!='.') return dfs(board,d+1);//prefill number skip

boolean[] flag=new boolean[10];
validate(board,i,j,flag);
for (int k=1; k<=9; k++) {
if (flag[k]) {
board[i][j]=(char)('0'+k);
if (dfs(board,d+1)) return true;
}
}
board[i][j]='.'; //if can not solve, in the wrong path, change back to '.' and out
return false;
}
private void validate(char[][] board, int i, int j, boolean[] flag) {
Arrays.fill(flag,true);
for (int k=0; k<9; k++) {
if (board[i][k]!='.') flag[board[i][k]-'0']=false;
if (board[k][j]!='.') flag[board[k][j]-'0']=false;
int r=i/3*3+k/3;
int c=j/3*3+k%3;
if (board[r][c]!='.') flag[board[r][c]-'0']=false;
}
}
}``````

• This is beautiful!

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