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LeetCode-297-Serialize-and-Deserialize-Binary-Tree.java
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LeetCode-297-Serialize-and-Deserialize-Binary-Tree.java
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/*
Many solutions to this question:
1.Preorder, use an array to mark # of nulls
http://blog.csdn.net/ljiabin/article/details/49474445
5
/ \
4 7
/ /
3 2
/ /
-1 9
[5,4,7,3,null,2,null,-1,null,9,null,null,null,null,null,]
左右孩子分别为 2*(i-num)+1 和 2*(i-num)+2
2. Recursive
3.Serialize to JSON (not do it)
https://leetcode.com/discuss/66397/java-stack-based-solution-using-json
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Codec {
// 1.BFS (level order traversal)
public String serialize(TreeNode root) {
if (root == null) return "";
Queue<TreeNode> queue = new LinkedList<TreeNode>();
queue.offer(root);
StringBuilder sb = new StringBuilder();
while(!queue.isEmpty()){
TreeNode curr = queue.poll();
if(curr == null){
sb.append("#").append(",");
}else{
sb.append(curr.val).append(",");
queue.offer(curr.left);
queue.offer(curr.right);
}
}
if(sb.length() > 0) sb.deleteCharAt(sb.length() - 1);
return sb.toString();
}
// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
if (data == null || data.length() == 0) return null;
String[] strs = data.split(",");
Queue<TreeNode> queue = new LinkedList<>();
TreeNode root = new TreeNode(Integer.parseInt(strs[0]));
queue.offer(root);
int count = 0;
while (!queue.isEmpty()) {
count++;
TreeNode curr = queue.poll();
if (!"#".equals(strs[count])) {
curr.left = new TreeNode(Integer.parseInt(strs[count]));
queue.offer(curr.left);
}
count++;
if (!"#".equals(strs[count])) {
curr.right = new TreeNode(Integer.parseInt(strs[count]));
queue.offer(curr.right);
}
}
return root;
}
// 2.Recursive
// public String serialize(TreeNode root) {
// if (root == null) return "#";
// return root.val + "," + serialize(root.left) + "," + serialize(root.right);
// }
// public TreeNode deserialize(String data) {
// String[] arr = data.split(",");
// int[] loc = new int[1];
// return deserialize(arr, loc);
// }
// private TreeNode deserialize(String[] arr, int[] loc) {
// if ("#".equals(arr[loc[0]])) {
// loc[0]++;
// return null;
// }
// TreeNode curr = new TreeNode(Integer.parseInt(arr[loc[0]]));
// loc[0]++;
// curr.left = deserialize(arr, loc);
// curr.right = deserialize(arr, loc);
// return curr;
// }
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));