圖valid-sudoku-leetcode練習題

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

/**
 * 判斷一個 9x9 的數獨是否有效。只需要根據以下規則，驗證已經填入的數字是否有效即可。
 * <p>
 * 數字 1-9 在每一行只能出現一次。
 * 數字 1-9 在每一列只能出現一次。
 * 數字 1-9 在每一個以粗實線分隔的 3x3 宮內只能出現一次。
 * <p>
 * 數獨部分空格內已填入了數字，空白格用 '.' 表示。
 * <p>
 * 示例 1:
 * <p>
 * 輸入:
 * [
 * ["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"]
 * ]
 * 輸出: true
 * 示例 2:
 * <p>
 * 輸入:
 * [
 *   ["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"]
 * ]
 * 輸出: false
 * 解釋: 除了第一行的第一個數字從 5 改爲 8 以外，空格內其他數字均與 示例1 相同。
 * 但由於位於左上角的 3x3 宮內有兩個 8 存在, 因此這個數獨是無效的。
 * 說明:
 * <p>
 * 一個有效的數獨（部分已被填充）不一定是可解的。
 * 只需要根據以上規則，驗證已經填入的數字是否有效即可。
 * 給定數獨序列只包含數字 1-9 和字符 '.' 。
 * 給定數獨永遠是 9x9 形式的。
 * <p>
 * 來源：力扣（LeetCode）
 * 鏈接：https://leetcode-cn.com/problems/valid-sudoku
 * 著作權歸領釦網絡所有。商業轉載請聯繫官方授權，非商業轉載請註明出處。
 */
public class Solution {
    public boolean isValidSudoku(char[][] board) {
        List<HashMap<Integer, Integer>> rowMap = new ArrayList<>();
        List<HashMap<Integer, Integer>> colMap = new ArrayList<>();
        List<HashMap<Integer, Integer>> squareMap = new ArrayList<>();
        // 初始化
        for (int i = 0; i < board.length; i++) {
            rowMap.add(new HashMap<>(9));
            colMap.add(new HashMap<>(9));
            squareMap.add(new HashMap<>(9));
        }
        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[i].length; j++) {
                char currentChar = board[i][j];
                if (currentChar != '.') {
                    int currentNumber = currentChar - '0';
                    // 行
                    HashMap<Integer, Integer> currentRow = rowMap.get(i);
                    currentRow.put(currentNumber, currentRow.getOrDefault(currentNumber, 0) + 1);
                    // 列
                    HashMap<Integer, Integer> currentCol = colMap.get(j);
                    currentCol.put(currentNumber, currentCol.getOrDefault(currentNumber, 0) + 1);
                    // 方格子
                    int squareIndex = (i / 3) * 3 + j / 3;
                    HashMap<Integer, Integer> currentSquare = squareMap.get(squareIndex);
                    currentSquare.put(currentNumber, currentSquare.getOrDefault(currentNumber, 0) + 1);
                    // 判斷異常情況
                    if (currentRow.get(currentNumber) > 1 || currentCol.get(currentNumber) > 1 || currentSquare.get(currentNumber) > 1) {
                        return false;
                    }
                }
            }
        }
        return true;
    }

    public static void main(String[] args) {
        char[][] board = {
                {'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'}};
        Solution solution = new Solution();
        System.out.println(solution.isValidSudoku(board));
    }
}

 

思想：

int squareIndex = (i / 3) * 3 + j / 3;