Leetcode37. 解数独

题目传送地址: ​​https://leetcode.cn/problems/sudoku-solver/​​

好开心，这道题解出来了

代码如下：

public static void solveSudoku(char[][] board) {
        Map<String, String> indexMap = initBlank(board);
        HashMap<String, Set<Integer>> map = new HashMap<>();
        int rowIndex = 0, colIndex = 0;
        while (rowIndex < 9 && colIndex < 9) {
            if (board[rowIndex][colIndex] != '.') {
                if (colIndex < 8) {
                    colIndex++;
                    continue;
                } else {
                    rowIndex++;
                    colIndex = 0;
                }
                continue;
            }
            if (fillUnit(board, rowIndex, colIndex, map)) { //如果填充成功
                if (colIndex < 8) {
                    colIndex++;
                    continue;
                } else {
                    rowIndex++;
                    colIndex = 0;
                }
            } else {
                map.remove(rowIndex+":"+colIndex);
                String lastIndex = indexMap.get(rowIndex + ":" + colIndex);
                String[] split = lastIndex.split(":");
                int lastRowIndex = Integer.parseInt(split[0]);
                int lastColIndex = Integer.parseInt(split[1]);
                char c = board[lastRowIndex][lastColIndex];
                Set<Integer> set = map.get(lastIndex);
                set.remove(c - '0');
                map.put(lastIndex, set);
                board[lastRowIndex][lastColIndex] = '.';
                rowIndex = lastRowIndex;
                colIndex = lastColIndex;
                continue;
            }
        }
    }

    //初始化map以后，我们就可以根据map获取上一个空白位置的坐标
    public static Map<String, String> initBlank(char[][] board) {
        HashMap<String, String> map = new HashMap<>();
        String lastIndex = "";
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i][j] == '.') {
                    map.put(i + ":" + j, lastIndex);
                    lastIndex = i + ":" + j;
                }
            }
        }
        return map;
    }


    public static boolean fillUnit(char[][] board, int i, int j, HashMap<String, Set<Integer>> map) {
        Set<Integer> set = getList(board, i, j);
        Set<Integer> set1 = map.get(i + ":" + j);
        if(set1!=null){
            set.retainAll(set1);
        }
        if (set.isEmpty()) {
            return false;
        }
        map.put(i + ":" + j, set);
        Iterator<Integer> iterator = set.iterator();
        Integer num = iterator.next();
        char c = String.valueOf(num).charAt(0);
        board[i][j] = c;
        return true;
    }


    public static Set<Integer> getList(char[][] board, int i, int j) {
        Set<Integer> set = new HashSet<>();
        for (int n = 1; n < 10; n++) {
            set.add(n);
        }
        //行内不能重复
        for (int n = 0; n < 9; n++) {
            if(board[i][n]!='.'){
                set.remove(board[i][n] - '0');
            }
        }
        //列内不能重复
        for (int m = 0; m < 9; m++) {
            if(board[m][j]!='.'){
                set.remove(board[m][j] - '0');
            }
        }
        //九宫格内不能重复
        int i1 = i - i % 3;
        int j1 = j - j % 3;
        for(int m=i1;m<i1+3;m++){
            for(int n=j1;n<j1+3;n++){
                if(board[m][n]!='.'){
                    set.remove(board[m][n] - '0');
                }
            }
        }
        return set;
    }