297. Serialize and Deserialize Binary Tree
BFS
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Codec { 11 12 // Encodes a tree to a single string. 13 public String serialize(TreeNode root) { 14 if (root == null) return ""; 15 Queue<TreeNode> queue = new LinkedList<>(); 16 queue.offer(root); 17 int size = queue.size(); 18 StringBuilder sb = new StringBuilder(); 19 while(!queue.isEmpty()){ 20 for(int i = 0; i < size; i++){ 21 TreeNode node = queue.poll(); 22 if(node != null){ 23 sb.append(node.val); 24 sb.append(" "); 25 }else{ 26 sb.append("n "); 27 continue; 28 } 29 30 queue.offer(node.left); 31 queue.offer(node.right); 32 } 33 size = queue.size(); 34 } 35 return sb.toString(); 36 37 38 } 39 40 // Decodes your encoded data to tree. 41 public TreeNode deserialize(String data) { 42 if(data.length() == 0) return null; 43 String[] strs = data.trim().split(" "); 44 Queue<TreeNode> queue = new LinkedList<>(); 45 TreeNode root = new TreeNode(Integer.parseInt(strs[0])); 46 queue.offer(root); 47 int size = queue.size(); 48 int index = 1; 49 while(!queue.isEmpty()){ 50 for(int i = 0; i < size; i++){ 51 TreeNode node = queue.poll(); 52 if(strs[index].equals("n")){ 53 node.left = null; 54 index++; 55 }else{ 56 TreeNode left = new TreeNode(Integer.parseInt(strs[index])); 57 node.left = left; 58 queue.offer(left); 59 index++; 60 } 61 if(strs[index].equals("n")){ 62 node.right = null; 63 index++; 64 }else{ 65 TreeNode right = new TreeNode(Integer.parseInt(strs[index])); 66 node.right = right; 67 queue.offer(right); 68 index++; 69 } 70 } 71 size = queue.size(); 72 } 73 return root; 74 } 75 } 76 77 // Your Codec object will be instantiated and called as such: 78 // Codec codec = new Codec(); 79 // codec.deserialize(codec.serialize(root));
