Solution Leetcode and Explaination Every single line

Author: Github-Saurabh0

70. Serialize and Deserialize Binary Tree/Codec.java

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+public class Codec {
+ 
+ // Serialize → Tree to String
+ public String serialize(TreeNode root) {
+ if (root == null) return "null";
+
+ StringBuilder sb = new StringBuilder();
+ Queue<TreeNode> q = new LinkedList<>();
+ q.offer(root);
+
+ while (!q.isEmpty()) {
+ TreeNode node = q.poll();
+ if (node == null) {
+ sb.append("null,");
+ continue;
+ }
+ sb.append(node.val).append(",");
+ q.offer(node.left);
+ q.offer(node.right);
+ }
+
+ return sb.toString();
+ }
+
+ // Deserialize → String to Tree
+ public TreeNode deserialize(String data) {
+ if (data.equals("null")) return null;
+
+ String[] vals = data.split(",");
+ TreeNode root = new TreeNode(Integer.parseInt(vals[0]));
+ Queue<TreeNode> q = new LinkedList<>();
+ q.offer(root);
+ int i = 1;
+
+ while (!q.isEmpty()) {
+ TreeNode curr = q.poll();
+ if (!vals[i].equals("null")) {
+ curr.left = new TreeNode(Integer.parseInt(vals[i]));
+ q.offer(curr.left);
+ }
+ i++;
+ if (!vals[i].equals("null")) {
+ curr.right = new TreeNode(Integer.parseInt(vals[i]));
+ q.offer(curr.right);
+ }
+ i++;
+ }
+
+ return root;
+ }
+}

70. Serialize and Deserialize Binary Tree/Program Explaination.txt

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+LeetCode 297 – Serialize and Deserialize Binary Tree 
+
+public class Codec {
+ 
+ // Serialize → Tree to String
+ public String serialize(TreeNode root) {
+ if (root == null) return "null";
+
+ StringBuilder sb = new StringBuilder();
+ Queue<TreeNode> q = new LinkedList<>();
+ q.offer(root);
+
+ while (!q.isEmpty()) {
+ TreeNode node = q.poll();
+ if (node == null) {
+ sb.append("null,");
+ continue;
+ }
+ sb.append(node.val).append(",");
+ q.offer(node.left);
+ q.offer(node.right);
+ }
+
+ return sb.toString();
+ }
+
+ // Deserialize → String to Tree
+ public TreeNode deserialize(String data) {
+ if (data.equals("null")) return null;
+
+ String[] vals = data.split(",");
+ TreeNode root = new TreeNode(Integer.parseInt(vals[0]));
+ Queue<TreeNode> q = new LinkedList<>();
+ q.offer(root);
+ int i = 1;
+
+ while (!q.isEmpty()) {
+ TreeNode curr = q.poll();
+ if (!vals[i].equals("null")) {
+ curr.left = new TreeNode(Integer.parseInt(vals[i]));
+ q.offer(curr.left);
+ }
+ i++;
+ if (!vals[i].equals("null")) {
+ curr.right = new TreeNode(Integer.parseInt(vals[i]));
+ q.offer(curr.right);
+ }
+ i++;
+ }
+
+ return root;
+ }
+}
+
+Explanation
+🔸 serialize() – Tree ko string mein convert karta hai
+
+if (root == null) return "null";
+🔹 Agar root hi null hai to null string return karo.
+
+StringBuilder sb = new StringBuilder();
+Queue<TreeNode> q = new LinkedList<>();
+🔹 Level order ke liye queue banayi.
+
+q.offer(root);
+🔹 Root node queue mein daala.
+
+while (!q.isEmpty())
+🔹 Jab tak queue khali na ho
+
+TreeNode node = q.poll();
+🔹 Queue ka front node nikala.
+
+if (node == null)
+ sb.append("null,");
+🔹 Null node mila toh "null" likh diya.
+
+else:
+ sb.append(node.val).append(",");
+ q.offer(node.left);
+ q.offer(node.right);
+🔹 Value likhi aur uske dono children ko queue mein daal diya.
+🔸 deserialize() – String ko tree mein wapas convert karta hai
+
+if (data.equals("null")) return null;
+🔹 Agar string hi null thi, return null root.
+
+String[] vals = data.split(",");
+🔹 Saare values ko comma ke basis par split kiya.
+
+TreeNode root = new TreeNode(Integer.parseInt(vals[0]));
+Queue<TreeNode> q = new LinkedList<>();
+q.offer(root);
+int i = 1;
+🔹 Root node create ki aur index 1 se traverse shuru kiya.
+
+while (!q.isEmpty())
+🔹 Jab tak queue khali na ho
+
+TreeNode curr = q.poll();
+🔹 Queue ka front nikala
+
+if (!vals[i].equals("null"))
+ curr.left = new TreeNode(Integer.parseInt(vals[i]));
+ q.offer(curr.left);
+
+i++;
+
+if (!vals[i].equals("null"))
+ curr.right = new TreeNode(Integer.parseInt(vals[i]));
+ q.offer(curr.right);
+
+i++;
+🔹 Left & right child assign kiya aur queue mein daal diya.
+
+Example:
+Input: root = [1,2,3,null,null,4,5]
+
+serialize() → "1,2,3,null,null,4,5,null,null,null,null,"
+deserialize() → Tree structure wapas same ban jaata hai
+
+Time and Space Complexity
+Operation	Time	Space
+Serialize	O(n)	O(n)
+Deserialize	O(n)	O(n)
+
+🔗 Facing any issue or want more Java tricks?
+https://www.linkedin.com/in/saurabh884095/