leetcode37-解数独

解数独

• 回溯+哈希

使用哈希表记录行、列和块的状态，然后对所有空缺的位置进行0-9的回溯。

class Solution {
    boolean line[][] = new boolean[9][9];
    boolean column[][] = new boolean[9][9];
    boolean blocks[][][] = new boolean[3][3][9];
    boolean isValid = false;
    List<int[]> pos = new ArrayList<>();
    public void solveSudoku(char[][] board) {
        for(int i = 0; i < 9; i++){
            for(int j = 0; j < 9; j++){
                if(board[i][j] == '.')
                    pos.add(new int[]{i, j});
                else{
                    int num = board[i][j]-'1';
                    line[i][num] = column[j][num] = blocks[i/3][j/3][num] = true;
                }
            }
        }
        dfs(board, 0);
    }
    public void dfs(char[][] board, int k){
        if(k == pos.size()){
            isValid = true;
            return;
        }
        int[] p = pos.get(k);
        int x = p[0], y = p[1];
        for(int i = 0; i < 9; i++){
            if(!line[x][i] && !column[y][i] && !blocks[x/3][y/3][i] && !isValid){
                board[x][y] = (char)(i+'1');
                line[x][i] = column[y][i] = blocks[x/3][y/3][i] = true;
                dfs(board, k+1);
                line[x][i] = column[y][i] = blocks[x/3][y/3][i] = false;
            }
        }
    }
}