add 773

Author: fishercoder1534

Diff for: README.md

@@ -745,6 +745,7 @@ _If you like this project, please leave me a star._ ★
 | 779  | [K-th Symbol in Grammar](https://leetcode.com/problems/k-th-symbol-in-grammar/)                                                                                                               | [Solution](../master/src/main/java/com/fishercoder/solutions/_779.java)                                                                  |                                                                               | Medium                           |
 | 776  | [Split BST](https://leetcode.com/problems/split-bst/)                                                                                                                                         | [Solution](../master/src/main/java/com/fishercoder/solutions/_776.java)                                                                  |                                                                               | Medium                           | Recursion                                                            
 | 775  | [Global and Local Inversions](https://leetcode.com/problems/global-and-local-inversions/)                                                                                                     | [Solution](../master/src/main/java/com/fishercoder/solutions/_775.java)                                                                  |                                                                               | Medium                           | Array, Math                                                          
+| 773  | [Sliding Puzzle](https://leetcode.com/problems/sliding-puzzle/)                                                                                                                                         | [Solution](../master/src/main/java/com/fishercoder/solutions/_773.java)                                                                  |                                                                               | Hard                             | BFS
 | 771  | [Jewels and Stones](https://leetcode.com/problems/jewels-and-stones/)                                                                                                                         | [Solution](../master/src/main/java/com/fishercoder/solutions/_771.java)                                                                  |                                                                               | Easy                             |
 | 769  | [Max Chunks To Make Sorted](https://leetcode.com/problems/max-chunks-to-make-sorted/)                                                                                                         | [Solution](../master/src/main/java/com/fishercoder/solutions/_769.java)                                                                  |                                                                               | Medium                           | Array                                                                
 | 767  | [Reorganize String](https://leetcode.com/problems/reorganize-string/)                                                                                                                         | [Solution](../master/src/main/java/com/fishercoder/solutions/_767.java)                                                                  |                                                                               | Medium                           |

Diff for: src/main/java/com/fishercoder/solutions/_773.java

@@ -0,0 +1,65 @@
+package com.fishercoder.solutions;
+
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Set;
+
+public class _773 {
+    public static class Solution1 {
+        public int slidingPuzzle(int[][] board) {
+            String target = "123450";
+            StringBuilder sb = new StringBuilder();
+            for (int i = 0; i < 2; i++) {
+                for (int j = 0; j < 3; j++) {
+                    sb.append(board[i][j]);
+                }
+            }
+            Queue<String> q = new LinkedList<>();
+            String start = sb.toString();
+            q.offer(start);
+            Set<String> visited = new HashSet<>();
+            visited.add(start);
+            //since there are only 6 cells, we just use 0 through 5 to represent the positions:
+            //0, 1, 2
+            //3, 4, 5
+            //the swap positions, go from left to right, top to bottom
+            //swap[index] means the possible positions to swap when '0' is at position index
+            int[][] swap = new int[][]{
+                    {1, 3},
+                    {0, 4, 2},
+                    {1, 5},
+                    {0, 4},
+                    {3, 1, 5},
+                    {2, 4}
+            };
+            int level = 0;
+            while (!q.isEmpty()) {
+                int size = q.size();
+                for (int i = 0; i < size; i++) {
+                    String curr = q.poll();
+                    if (curr.equals(target)) {
+                        return level;
+                    }
+                    int index = curr.indexOf('0');
+                    for (int swapIndex : swap[index]) {
+                        sb.setLength(0);
+                        sb.append(curr);
+
+                        //swap
+                        sb.setCharAt(index, curr.charAt(swapIndex));
+                        sb.setCharAt(swapIndex, '0');
+
+                        String path = sb.toString();
+                        if (!visited.add(path)) {
+                            continue;
+                        }
+                        q.offer(path);
+                    }
+                }
+                level++;
+            }
+            return -1;
+        }
+    }
+}

Diff for: src/test/java/com/fishercoder/_773Test.java

@@ -0,0 +1,36 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._773;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class _773Test {
+    private static _773.Solution1 solution1;
+    private static int[][] board;
+
+    @BeforeEach
+    public void setup() {
+        solution1 = new _773.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        board = new int[][]{
+                {1, 2, 3},
+                {4, 0, 5}
+        };
+        assertEquals(1, solution1.slidingPuzzle(board));
+    }
+
+    @Test
+    public void test2() {
+        board = new int[][]{
+                {4, 1, 2},
+                {5, 0, 3}
+        };
+        assertEquals(5, solution1.slidingPuzzle(board));
+    }
+
+}