add 30 and update other solutions

Author: FreeTymeKiyan

src/main/java/com/freetymekiyan/algorithms/level/easy/CountAndSay.java

@@ -17,27 +17,26 @@
  * Tags: String
  * Similar Problems: (M) Encode and Decode Strings
  */
-
 class CountAndSay {
 
-    /**
-     * String. Simulate the process.
-     * Generate the next sequence.
-     * Repeat n-1 times.
-     */
-    public String countAndSay(int n) {
-        String res = "1";
-        while (n > 1) {
-            StringBuilder s = new StringBuilder();
-            for (int i = 0, j = i; i < res.length(); i = j) {
-                while (j < res.length() && res.charAt(i) == res.charAt(j)) {
-                    j++;
-                }
-                s.append(j - i).append(res.charAt(i));
-            }
-            res = s.toString();
-            n--;
-        }
-        return res;
+  /**
+   * String. Simulate the process.
+   * Generate the next sequence.
+   * Repeat n-1 times.
+   */
+public String countAndSay(int n) {
+  String res = "1";
+  while (n > 1) {
+    StringBuilder s = new StringBuilder();
+    for (int i = 0, j = i; i < res.length(); i = j) {
+      while (j < res.length() && res.charAt(i) == res.charAt(j)) {
+        j++;
+      }
+      s.append(j - i).append(res.charAt(i));
     }
+    res = s.toString();
+    n--;
+  }
+  return res;
+}
 }

src/main/java/com/freetymekiyan/algorithms/level/easy/ValidSudoku.java

@@ -5,132 +5,131 @@
 
 /**
  * Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.
- *
+ * <p>
  * The Sudoku board could be partially filled, where empty cells are filled
  * with the character '.'.
- *
+ * <p>
  * Note:
  * A valid Sudoku board (partially filled) is not necessarily solvable. Only
  * the filled cells need to be validated.
- *
+ * <p>
  * Tags: Hash table
  */
 class ValidSudoku {
-    public static void main(String[] args) {
-        ValidSudoku v = new ValidSudoku();
-        
-        char[][] board = new char[9][9];
-        for (int i = 0; i < board.length; i++) {
-            for (int j = 0; j < board[i].length; j++) {
-                if (i == 0 && j == 0) {
-                    board[i][j] = '.';
-                } else if (i == 0 && j != 0) {
-                    board[i][j] = (char)('0' + j + 1);
-                } else {
-                    board[i][j] = '.';
-                }
-            }
+  public static void main(String[] args) {
+    ValidSudoku v = new ValidSudoku();
+
+    char[][] board = new char[9][9];
+    for (int i = 0; i < board.length; i++) {
+      for (int j = 0; j < board[i].length; j++) {
+        if (i == 0 && j == 0) {
+          board[i][j] = '.';
+        } else if (i == 0 && j != 0) {
+          board[i][j] = (char) ('0' + j + 1);
+        } else {
+          board[i][j] = '.';
         }
-        v.printBoard(board);
-        System.out.println(v.isValidSudoku(board));
+      }
     }
-
-    public boolean isValidSudoku(char[][] board) {
-        boolean[][] row = new boolean[9][9];
-        boolean[][] col = new boolean[9][9];
-        boolean[][] box = new boolean[9][9];
-
-        for (int i = 0; i < 9; i++) {
-            for (int j = 0; j < 9; j++) {
-                if (board[i][j] != '.') {
-                    int num = board[i][j] - '0' - 1;
-                    int k = i / 3 * 3 + j / 3;
-                    if (row[i][num] || col[j][num] || box[k][num]) {
-                        return false;
-                    }
-                    row[i][num] = col[j][num] = box[k][num] = true;
-                }
-            }
+    v.printBoard(board);
+    System.out.println(v.isValidSudoku(board));
+  }
+
+  public boolean isValidSudoku(char[][] board) {
+    boolean[][] row = new boolean[9][9];
+    boolean[][] col = new boolean[9][9];
+    boolean[][] box = new boolean[9][9];
+
+    for (int i = 0; i < 9; i++) {
+      for (int j = 0; j < 9; j++) {
+        if (board[i][j] != '.') {
+          int num = board[i][j] - '0' - 1;
+          int k = i / 3 * 3 + j / 3;
+          if (row[i][num] || col[j][num] || box[k][num]) {
+            return false;
+          }
+          row[i][num] = col[j][num] = box[k][num] = true;
         }
-        return true;
+      }
     }
+    return true;
+  }
+
+  /**
+   * Use three arrays of integers to do masking
+   */
+  public boolean isValidSudoku2(char[][] board) {
+    int[] row = new int[9];
+    int[] col = new int[9];
+    int[] sqr = new int[9];
+
+    for (int i = 0; i < 9; i++) {
+      for (int j = 0; j < 9; j++) {
+        if (board[i][j] != '.') {
+          int num = board[i][j] - '0';
+          if ((row[i] & 1 << num) > 0) return false; // already in row
+          else row[i] |= 1 << num;
+
+          if ((col[j] & 1 << num) > 0) return false;// already in col
+          else col[j] |= 1 << num;
+
+          int sqrIdx = (i - i % 3) + j / 3; // note the square idx
+          if ((sqr[sqrIdx] & 1 << num) > 0) return false; // already
+          else sqr[sqrIdx] |= 1 << num;
 
-    /**
-     * Use three arrays of integers to do masking
-     */
-    public boolean isValidSudoku2(char[][] board) {
-        int[] row = new int[9];
-        int[] col = new int[9];
-        int[] sqr = new int[9];
-
-        for (int i = 0; i < 9; i++){
-            for (int j = 0; j < 9; j++) {
-                if (board[i][j] != '.') {
-                    int num = board[i][j] - '0';
-                    if ((row[i] & 1 << num) > 0) return false; // already in row
-                    else row[i] |= 1 << num;
-
-                    if ((col[j] & 1 << num) > 0) return false;// already in col
-                    else col[j] |= 1 << num;
-
-                    int sqrIdx = (i - i % 3) + j / 3; // note the square idx
-                    if ((sqr[sqrIdx] & 1 << num) > 0) return false; // already
-                    else sqr[sqrIdx] |= 1 << num;
-
-                }
-            }
         }
-        return true;
-
+      }
     }
-
-    /**
-     * hashtable, index as key, mask as value
-     */
-    public boolean isValidSudoku3(char[][] board) {
-        Map<Integer, Integer> row = new HashMap<Integer, Integer>();
-        Map<Integer, Integer> col = new HashMap<Integer, Integer>();
-        Map<Integer, Integer> sqr = new HashMap<Integer, Integer>();
-
-        for (int i = 0; i < board.length; i++) {
-            for (int j = 0; j < board[i].length; j++) {
-                if (board[i][j] != '.') {
-                    int num = board[i][j] - '0';
-                    int rowMask = row.containsKey(i) ? row.get(i) : 0;
-                    if ((rowMask & 1 << num) > 0) {
-                        return false;
-                    } else {
-                        row.put(i, rowMask | 1 << num);
-                    }
-
-                    int colMask = col.containsKey(j) ? col.get(j) : 0;
-                    if ((colMask & 1 << num) > 0) {
-                        return false;
-                    } else {
-                        col.put(j, colMask | 1 << num);
-                    }
-
-                    int sqrIdx = (i - i % 3) + j / 3;
-                    int sqrMask = sqr.containsKey(sqrIdx) ? sqr.get(sqrIdx) : 0;
-                    if ((sqrMask & 1 << num) > 0) {
-                        return false;
-                    } else {
-                        sqr.put(sqrIdx, sqrMask | 1 << num);
-                    }
-                }
-            }
+    return true;
+  }
+
+  /**
+   * hashtable, index as key, mask as value
+   */
+  public boolean isValidSudoku3(char[][] board) {
+    Map<Integer, Integer> row = new HashMap<>();
+    Map<Integer, Integer> col = new HashMap<>();
+    Map<Integer, Integer> sqr = new HashMap<>();
+
+    for (int i = 0; i < board.length; i++) {
+      for (int j = 0; j < board[i].length; j++) {
+        if (board[i][j] != '.') {
+          int num = board[i][j] - '0';
+          int rowMask = row.containsKey(i) ? row.get(i) : 0;
+          if ((rowMask & 1 << num) > 0) {
+            return false;
+          } else {
+            row.put(i, rowMask | 1 << num);
+          }
+
+          int colMask = col.containsKey(j) ? col.get(j) : 0;
+          if ((colMask & 1 << num) > 0) {
+            return false;
+          } else {
+            col.put(j, colMask | 1 << num);
+          }
+
+          int sqrIdx = (i - i % 3) + j / 3;
+          int sqrMask = sqr.containsKey(sqrIdx) ? sqr.get(sqrIdx) : 0;
+          if ((sqrMask & 1 << num) > 0) {
+            return false;
+          } else {
+            sqr.put(sqrIdx, sqrMask | 1 << num);
+          }
         }
-
-        return true;
+      }
     }
 
-    private void printBoard(char[][] board) {
-        for (int i = 0; i < board.length; i++) {
-            for (int j = 0; j < board[i].length; j++) {
-                System.out.print(board[i][j] + " ");
-            }
-            System.out.println();
-        }
-        System.out.println("-----------------");
+    return true;
+  }
+
+  private void printBoard(char[][] board) {
+    for (int i = 0; i < board.length; i++) {
+      for (int j = 0; j < board[i].length; j++) {
+        System.out.print(board[i][j] + " ");
+      }
+      System.out.println();
     }
+    System.out.println("-----------------");
+  }
 }