在刷題的時候遇到了一個求解數獨的問題，用回溯法寫了以下程式碼，記錄一下，之後探究有沒有更好的演算法。
演算法思路： ①讀取待求解陣列，其中待填位置為0。 ②將所有待填位置的兩個座標（行列）和目前數字封裝起來壓入棧1中。 ③開一個棧2用於儲存目前確定的答案。 ④當棧1不為空的時候，取棧頂元素，從元素當前值加一開始依次到9判斷是否可以填入，若可以則將當前元素壓入棧2，否則壓回棧1並且取出棧2棧頂元素押回棧1； ⑤重複④，直到棧1為空。
java程式碼如下： public class Main {

    public static void main(String[] args) {         Stack<Index> stack = new Stack<>();         Stack<Index> stack2 = new Stack<>();         Scanner in = new Scanner(System.in);

        while (in.hasNext()) {             int[][] num = new int[9][9];             for (int i = 0; i < 9; i++) {

                for (int j = 0; j < 9; j++) {                     int t = in.nextInt();                     if (t == 0) {                         stack.push(new Index(0, i, j));                     }                     num[i][j] = t;
                }             }             while (!stack.isEmpty()) {                 Index top = stack.pop();                 int i = top.num + 1;                 for (; i <= 9; i++) {                     num[top.row][top.col] = i;                     if (isRight(top.row, top.col, num)) {                         top.num = i;                         break;                     }                 }                 if (i == 10 && !stack2.isEmpty()) { //沒答案                     num[top.row][top.col] = 0;                     top.num = 0;                     stack.push(top);                     stack.push(stack2.pop());                 } else {                     stack2.push(top);                 }
            }             for (int i = 0; i < 9; i++) {                 for (int j = 0; j < 8; j++) {                     System.out.print(num[i][j] + " ");                 }                 System.out.print(num[i][8]);                 System.out.println();             }         }     }
    private static boolean isRight(int row, int col, int[][] a) {         for (int i = 0; i < 9; i++) {             if (i == col || a[row][i] == 0) {                 continue;             }             if (a[row][i] == a[row][col]) {                 return false;             }         }         for (int i = 0; i < 9; i++) {             if (i == row || a[i][col] == 0) {                 continue;             }             if (a[i][col] == a[row][col]) {                 return false;             }         }         return true;     } }
class Index {     public int num;     public int row;     public int col;
    public Index(int num, int row, int col) {         this.num = num;         this.row = row;         this.col = col;     } }


執行示例：