Coursera Algorithms Programming Assignment 4: 8 Puzzle （100分）

  1 import java.util.ArrayList;
  2 /**
  3  * @author evasean www.cnblogs.com/evasean/
  4  */
  5 public class Board {
  6     private static final int BLANK = 0;
  7     private final int n;
  8     private int[][] blocks;
  9 
 10     public Board(int[][] inBlocks) {
 11         // construct a board from an n-by-n array of blocks
 12         // (where blocks[i][j] = block in row i, column j)
 13         n = inBlocks.length;
 14         blocks = new int[n][n];
 15         copy(blocks, inBlocks);
 16     }
 17 
 18     private void copy(int[][] toBlocks, int[][] fromBlocks) {
 19         for (int row = 0; row < n; row++)
 20             for (int col = 0; col < n; col++)
 21                 toBlocks[row][col] = fromBlocks[row][col];
 22     }
 23 
 24     public int dimension() {
 25         // board dimension n
 26         return n;
 27     }
 28 
 29     private int getRow(int value) {
 30         return (value - 1) / n;
 31     }
 32 
 33     private int getCol(int value) {
 34         return (value - 1) % n;
 35     }
 36 
 37     private int getValue(int row, int col) {
 38         return row * n + col + 1;
 39     }
 40 
 41     public int hamming() {
 42         // number of blocks out of place
 43         int hamming = 0;
 44         for (int row = 0; row < n; row++)
 45             for (int col = 0; col < n; col++)
 46                 if (blocks[row][col] != BLANK && blocks[row][col] != getValue(row, col))
 47                     hamming++;
 48         return hamming;
 49     }
 50 
 51     public int manhattan() {
 52         // sum of Manhattan distances between blocks and goal
 53         int manhattan = 0;
 54         for (int row = 0; row < n; row++)
 55             for (int col = 0; col < n; col++)
 56                 if (blocks[row][col] != BLANK && blocks[row][col] != getValue(row, col))
 57                     manhattan += Math.abs(getRow(blocks[row][col]) - row) + Math.abs(getCol(blocks[row][col]) - col);
 58         return manhattan;
 59     }
 60 
 61     public boolean isGoal() {
 62         // is this board the goal board?
 63         for (int row = 0; row < n; row++)
 64             for (int col = 0; col < n; col++)
 65                 if (blocks[row][col] != BLANK && blocks[row][col] != getValue(row, col))
 66                     return false;
 67         return true;
 68     }
 69 
 70     public Board twin() {
 71         // a board that is obtained by exchanging any pair of blocks
 72         Board twinBoard = new Board(blocks);
 73         int firRow = 0;
 74         int firCol = 0;
 75         if (blocks[firRow][firCol] == BLANK)
 76             firCol++;
 77         for (int row = 0; row < n; row++) {
 78             for (int col = 0; col < n; col++) {
 79                 if (blocks[row][col] != blocks[firRow][firCol] && blocks[row][col] != BLANK) {
 80                     twinBoard.swap(firRow, firCol, row, col);
 81                     return twinBoard;
 82                 }
 83             }
 84         }
 85         return twinBoard;
 86     }
 87 
 88     private void swap(int vRow, int vCol, int wRow, int wCol) {
 89         int t = blocks[vRow][vCol];
 90         blocks[vRow][vCol] = blocks[wRow][wCol];
 91         blocks[wRow][wCol] = t;
 92     }
 93 
 94     public boolean equals(Object y) {
 95         // does this board equal y?
 96         if (y == null)
 97             return false;
 98         if (y == this)
 99             return true;
100         if (y.getClass().isInstance(this)) {
101             Board yb = (Board) y;
102             if (yb.n != this.n)
103                 return false;
104             else {
105                 for (int row = 0; row < n; row++)
106                     for (int col = 0; col < n; col++)
107                         if (yb.blocks[row][col] != blocks[row][col])
108                             return false;
109                 return true;
110             }
111         } else
112             return false;
113     }
114 
115     public Iterable<Board> neighbors() {
116         // all neighboring boards
117         ArrayList<Board> neighbors = new ArrayList<Board>();
118         for (int row = 0; row < n; row++) {
119             for (int col = 0; col < n; col++) {
120                 if (blocks[row][col] == BLANK) {
121                     // 空白的位置分别与上下左右的元素交换一次位置就得到一个邻居board
122                     // 与上方元素互换
123                     if (row > 0) {
124                         Board neighborT = new Board(blocks);
125                         neighborT.swap(row, col, row - 1, col);
126                         neighbors.add(neighborT);
127                     }
128                     // 与下方元素互换
129                     if (row < n - 1) {
130                         Board neighborB = new Board(blocks);
131                         neighborB.swap(row, col, row + 1, col);
132                         neighbors.add(neighborB);
133                     }
134                     // 与左边元素互换
135                     if (col > 0) {
136                         Board neighborL = new Board(blocks);
137                         neighborL.swap(row, col, row, col - 1);
138                         neighbors.add(neighborL);
139                     }
140                     // 与右边元素互换
141                     if (col < n - 1) {
142                         Board neighborR = new Board(blocks);
143                         neighborR.swap(row, col, row, col + 1);
144                         neighbors.add(neighborR);
145                     }
146                 }
147             }
148         }
149         return neighbors;
150     }
151 
152     public String toString() {
153         // string representation of this board (in the output format specified
154         // below)
155         StringBuilder sb = new StringBuilder();
156         sb.append(n + "\n");
157         for (int row = 0; row < n; row++) {
158             for (int col = 0; col < n; col++) {
159                 //本来考虑到n<128时元素可能会很大，设置的是%6d，但是提交时不满足校验规则
160                 //校验规则要求必须是%2d，很奇怪的校验
161                 sb.append(String.format("%2d ", blocks[row][col]));
162             }
163             sb.append("\n");
164         }
165         return sb.toString();
166     }
167 
168     public static void main(String[] args) {
169 //         unit tests (not graded)
170 //         int[][] test = { { 0, 1}, {2,3 }};
171 //         Board b = new Board(test);
172 //         System.out.println(b);
173 //         System.out.println(b.hamming());
174 //         System.out.println(b.manhattan());
175     }
176 }

  1 import edu.princeton.cs.algs4.In;
  2 import edu.princeton.cs.algs4.MinPQ;
  3 import edu.princeton.cs.algs4.Stack;
  4 import edu.princeton.cs.algs4.StdOut;
  5 /**
  6  * @author evasean www.cnblogs.com/evasean/
  7  */
  8 public class Solver {
  9     
 10     private SearchNode currentNode;
 11     private SearchNode twincurrentNode;
 12     private Stack<Board> solution;
 13     
 14     private class SearchNode implements Comparable<SearchNode>{
 15         public Board board;
 16         public int moves;
 17         public SearchNode preSearchNode;
 18         
 19         public final int priority;
 20         
 21         public SearchNode(Board inboard, SearchNode inPreSearchNode){
 22             board = inboard;
 23             preSearchNode = inPreSearchNode;
 24             if(inPreSearchNode == null) moves = 0;    
 25             else moves = inPreSearchNode.moves + 1;
 26             priority = moves + board.manhattan();
 27         }
 28 
 29         @Override
 30         public int compareTo(SearchNode o) {
 31             return Integer.compare(this.priority, o.priority);
 32         }
 33     }
 34     
 35     
 36     public Solver(Board initial) {
 37         // find a solution to the initial board (using the A* algorithm)
 38         if(initial == null)
 39             throw new IllegalArgumentException("Constructor argument Board is null!");
 40         currentNode = new SearchNode(initial,null);
 41         twincurrentNode = new SearchNode(initial.twin(),null);
 42         MinPQ<SearchNode> priorityQueue = new MinPQ<SearchNode>();
 43         MinPQ<SearchNode> twinPriorityQueue = new MinPQ<SearchNode>();
 44         priorityQueue.insert(currentNode);
 45         twinPriorityQueue.insert(twincurrentNode);
 46         while(true){
 47             currentNode = priorityQueue.delMin();
 48             if(currentNode.board.isGoal()) break;
 49             putNeighBorsIntoPQ(currentNode,priorityQueue);
 50             
 51             twincurrentNode = twinPriorityQueue.delMin();
 52             if(twincurrentNode.board.isGoal()) break;
 53             putNeighBorsIntoPQ(twincurrentNode,twinPriorityQueue);
 54         }
 55     }
 56     
 57     private void putNeighBorsIntoPQ(SearchNode searchNode, MinPQ<SearchNode> pq){
 58         Iterable<Board> neighbors = searchNode.board.neighbors();
 59         for(Board neighbor : neighbors){
 60             //只有在当前搜索节点的邻居们的borad不与当前节点的preSearchNode的borad相同
 61             //才将该邻居放入优先队列
 62             
 63             if(searchNode.preSearchNode==null || !neighbor.equals(searchNode.preSearchNode.board))
 64                 pq.insert(new SearchNode(neighbor,searchNode));
 65         }
 66     }
 67 
 68     public boolean isSolvable() {
 69         // is the initial board solvable?
 70         return currentNode.board.isGoal();
 71     }
 72 
 73     public int moves() {
 74         // min number of moves to solve initial board; -1 if unsolvable
 75         if(currentNode.board.isGoal())
 76             return currentNode.moves;
 77         else
 78             return -1;
 79     }
 80 
 81     public Iterable<Board> solution() {
 82         // sequence of boards in a shortest solution; null if unsolvable
 83         if(currentNode.board.isGoal()){
 84             solution = new Stack<Board>();
 85             SearchNode node = currentNode;
 86             while(node != null){
 87                 solution.push(node.board);
 88                 node = node.preSearchNode;
 89             }
 90             return solution;
 91         }else
 92             return null;
 93     }
 94 
 95     public static void main(String[] args) {
 96         // solve a slider puzzle (given below)
 97         // create initial board from file
 98 //        In in = new In(args[0]);
 99         In in = new In("8puzzle/puzzle3x3-unsolvable.txt"); //本地测试之用
100         int n = in.readInt();
101         int[][] blocks = new int[n][n];
102         for (int i = 0; i < n; i++)
103             for (int j = 0; j < n; j++)
104                 blocks[i][j] = in.readInt();
105         Board initial = new Board(blocks);
106 
107         // solve the puzzle
108         Solver solver = new Solver(initial);
109 
110         // print solution to standard output
111         if (!solver.isSolvable())
112             StdOut.println("No solution possible");
113         else {
114             StdOut.println("Minimum number of moves = " + solver.moves());
115             for (Board board : solver.solution())
116                 StdOut.println(board);
117         }
118     }
119 }