有效的數獨 的題目是:
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。
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。
image
上圖是一個部分填充的有效的數獨。
數獨部分空格內已填入了數字，空白格用 '.' 表示。
示例 1:
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: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 改為 8 以外，空格內其他數字均與 示例1 相同。
但由于位于左上角的 3x3 宮內有兩個 8 存在, 因此這個數獨是無效的。
說明: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。
題目比較長，沒有玩過數獨的可能還要理解一下這個題目，其實就是判斷橫向的 9 個數組，豎向的 9 個數組和 9 個 3 * 3 的小方格里都沒有重復的元素。有點繞的是遍歷二維數組時怎么把每個元素存入對應的 3 * 3 的小方塊里。對應子方塊的 index 的計算方法為：
//horizonIndex 為遍歷時橫向 index，verticalIndex 為垂直 index
int cubeIndex = verticalIndex / 3 + (horizonIndex / 3) * 3;
然后還要利用Set 容器去重復的特性，Set.add(T item)會返回一個 boolean 值，為 true 就是容器里不存在同樣的元素，false 就是存在，可以做為判斷數獨是否有效的簡便方法。
其他沒有什么好說的，放代碼：
public static boolean isValidSudoku(char[][] board) {
List<Set<Character>> horizonList = new ArrayList<>(9);
List<Set<Character>> verticalList = new ArrayList<>(9);
List<Set<Character>> cubeList = new ArrayList<>(9);
for (int i = 0; i < 9; i++) {
horizonList.add(new HashSet<Character>());
verticalList.add(new HashSet<Character>());
cubeList.add(new HashSet<Character>());
}
for (int j = 0; j < 9; j++) {
for (int k = 0; k < 9; k++) {
char c = board[j][k];
if(c == '.'){
continue;
}
if(!horizonList.get(j).add(c)){
return false;
}
if(!verticalList.get(k).add(c)){
return false;
}
int cubeIndex = k / 3 + (j / 3) * 3;
Set<Character> set = cubeList.get(cubeIndex);
if(!set.add(c)){
return false;
}
}
}
return true;
