LeetCode/src/explore/array/ValidSudoku.java at master · GeniusDSY/LeetCode · GitHub

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package explore.array;

import java.util.HashMap;

/**
 * @author :DengSiYuan
 * @date :2020/2/29 17:38
 * @desc :36. 有效的数独
 * 【题目】
 *      判断一个 9x9 的数独是否有效。只需要根据以下规则，验证已经填入的数字是否有效即可。
 *          数字 1-9 在每一行只能出现一次。
 *          数字 1-9 在每一列只能出现一次。
 *          数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。
 *      上图是一个部分填充的有效的数独。
 *      数独部分空格内已填入了数字，空白格用 '.' 表示。
 * 【示例】
 *      输入:
 *          [
 *              ["5","3",".",".","7",".",".",".","."],
 *              ["6",".",".","1","9","5",".",".","."],
 *              [".","9","8",".",".",".",".","6","."],
 *              ["8",".",".",".","6",".",".",".","3"],
 *              ["4",".",".","8",".","3",".",".","1"],
 *              ["7",".",".",".","2",".",".",".","6"],
 *              [".","6",".",".",".",".","2","8","."],
 *              [".",".",".","4","1","9",".",".","5"],
 *              [".",".",".",".","8",".",".","7","9"]
 *          ]
 *      输出: true
 *
 *      输入:
 *          [
 *              ["8","3",".",".","7",".",".",".","."],
 *              ["6",".",".","1","9","5",".",".","."],
 *              [".","9","8",".",".",".",".","6","."],
 *              ["8",".",".",".","6",".",".",".","3"],
 *              ["4",".",".","8",".","3",".",".","1"],
 *              ["7",".",".",".","2",".",".",".","6"],
 *              [".","6",".",".",".",".","2","8","."],
 *              [".",".",".","4","1","9",".",".","5"],
 *              [".",".",".",".","8",".",".","7","9"]
 *          ]
 *      输出: false
 *      解释: 除了第一行的第一个数字从 5 改为 8 以外，空格内其他数字均与 示例1 相同。
 *      但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。
 * 【说明】
 *      一个有效的数独（部分已被填充）不一定是可解的。
 *      只需要根据以上规则，验证已经填入的数字是否有效即可。
 *      给定数独序列只包含数字 1-9 和字符 '.' 。
 *      给定数独永远是 9x9 形式的。
 */
public class ValidSudoku {

    public boolean isValidSudoku(char[][] board) {
        // init data
        HashMap<Integer, Integer>[] rows = new HashMap[9];
        HashMap<Integer, Integer>[] columns = new HashMap[9];
        HashMap<Integer, Integer>[] boxes = new HashMap[9];
        for (int i = 0; i < 9; i++) {
            rows[i] = new HashMap<>();
            columns[i] = new HashMap<>();
            boxes[i] = new HashMap<>();
        }

        // validate a board
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                char num = board[i][j];
                if (num != '.') {
                    int n = (int)num;
                    int boxIndex = (i / 3 ) * 3 + j / 3;

                    // keep the current cell value
                    rows[i].put(n, rows[i].getOrDefault(n, 0) + 1);
                    columns[j].put(n, columns[j].getOrDefault(n, 0) + 1);
                    boxes[boxIndex].put(n, boxes[boxIndex].getOrDefault(n, 0) + 1);

                    // check if this value has been already seen before
                    if (rows[i].get(n) > 1 || columns[j].get(n) > 1 || boxes[boxIndex].get(n) > 1) {
                        return false;
                    }
                }
            }
        }
        return true;
    }

}