二刷优化37

Author: diguage

docs/0037-sudoku-solver.adoc

@@ -57,6 +57,15 @@ include::{sourcedir}/_0037_SudokuSolver.java[tag=answer]
 include::{sourcedir}/_0037_SudokuSolver_2.java[tag=answer]
 ----
 --
+
+二刷（引入步进）::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0037_SudokuSolver_21.java[tag=answer]
+----
+--
 ====
 
 == 参考资料

src/main/java/com/diguage/algo/leetcode/_0037_SudokuSolver_21.java

@@ -0,0 +1,106 @@
+package com.diguage.algo.leetcode;
+
+import static com.diguage.util.Printers.printMatrix;
+
+public class _0037_SudokuSolver_21 {
+  // tag::answer[]
+
+  /**
+   * * @author D瓜哥 · https://www.diguage.com
+   * * @since 2024-09-11 10:59:08
+   */
+  public void solveSudoku(char[][] board) {
+    backtracking(board, 0);
+  }
+
+  private boolean backtracking(char[][] board, int step) {
+    int row = step / board.length;
+    int column = step % board.length;
+    for (int r = row; r < board.length; r++) {
+      for (int c = column; c < board[r].length; c++) {
+        if (board[r][c] != '.') {
+          return backtracking(board, step + 1);
+        }
+        // 根据限制条件，筛选出可选字符，否则重复判断
+        char[] chars = selectChars(board, r, c);
+        for (char sc : chars) {
+          board[r][c] = sc;
+          printMatrix(board);
+          if (backtracking(board, step + 1)) {
+            return true;
+          }
+          board[r][c] = '.';
+        }
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private char[] selectChars(char[][] board, int row, int column) {
+    char[] chars = new char[9];
+    int length = 9;
+    for (int i = 0; i < chars.length; i++) {
+      chars[i] = (char) ('1' + i);
+    }
+    for (int i = 0; i < board.length; i++) {
+      char c = board[i][column];
+      if (c != '.' && chars[c - '1'] != '.') {
+        chars[c - '1'] = '.';
+        length--;
+        if (length == 0) {
+          return new char[0];
+        }
+      }
+    }
+    for (int i = 0; i < board[row].length; i++) {
+      char c = board[row][i];
+      if (c != '.' && chars[c - '1'] != '.') {
+        chars[c - '1'] = '.';
+        length--;
+        if (length == 0) {
+          return new char[0];
+        }
+      }
+    }
+    row = (row / 3) * 3;
+    column = (column / 3) * 3;
+    for (int i = row; i < row + 3; i++) {
+      for (int j = column; j < column + 3; j++) {
+        char c = board[i][j];
+        if (c != '.' && chars[c - '1'] != '.') {
+          chars[c - '1'] = '.';
+          length--;
+          if (length == 0) {
+            return new char[0];
+          }
+        }
+      }
+    }
+    char[] result = new char[length];
+    for (int i = chars.length - 1; i >= 0; i--) {
+      if (chars[i] != '.') {
+        result[--length] = chars[i];
+      }
+    }
+    return result;
+  }
+
+  // end::answer[]
+  public static void main(String[] args) {
+    char[][] b1 = {
+      {'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'}
+    };
+    _0037_SudokuSolver_21 solution = new _0037_SudokuSolver_21();
+    solution.solveSudoku(b1);
+    printMatrix(b1);
+  }
+}