Added solution for - Reverse Odd Levels Of Binary Tree (LC#2415)

Java/ReverseOddLevelsOfBinaryTree.java

@@ -0,0 +1,57 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class ReverseOddLevelsOfBinaryTree {
+ /**
+ Store all the level's data in a list by simply any traversal(pre-order here)
+ Then again traverse the tree and when found the odd level,
+ change the root data with the last element of the level-list and remove the last item
+ */
+ public TreeNode reverseOddLevels(TreeNode root) {
+ List<List<Integer>> list = new ArrayList<>();
+ tra(list, root, 0);
+ modify(list, root, 0);
+ return root;
+ }
+ private void modify(List<List<Integer>> res, TreeNode root, int level){
+ if(root == null) return;
+
+ // Odd level
+ if((level%2) != 0){
+
+ // Modify root data with last item of list, and then remove the last item
+ List<Integer> lvlArr = res.get(level);
+ root.val = lvlArr.get(lvlArr.size()-1);
+ lvlArr.remove(lvlArr.size()-1);
+ }
+
+ modify(res,root.left,level+1);
+ modify(res,root.right,level+1);
+ }
+
+ // generate list with level-order items
+ private void tra(List<List<Integer>> res, TreeNode root, int level){
+ if(root == null) return;
+
+ if(level >= res.size())
+ res.add(new ArrayList<>());
+
+ res.get(level).add(root.val);
+ tra(res,root.left,level+1);
+ tra(res,root.right,level+1);
+ }
+
+ static class TreeNode{
+ int val;
+ TreeNode left;
+ TreeNode right;
+
+ public TreeNode() {}
+ TreeNode(int val) { this.val = val; }
+ public TreeNode(int val, TreeNode left, TreeNode right) {
+ this.val = val;
+ this.left = left;
+ this.right = right;
+ }
+ }
+}

README.md

@@ -260,6 +260,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 98 | [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/) | [Javascript](./JavaScript/98.Validate-Binary-Search-Tree.js) | _O(log(n))_ | _O(log(n))_ | Medium | Binary Tree |
 | 684 | [Redundant Connection](https://leetcode.com/problems/redundant-connection/) | [Java](./Java/Redundant-Connection/redundant-connection.java) | _O(N)_ | _O(N)_ | Medium | Tree, Union Find |
 | 102 | [Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/) |[C++](./C++/Binary-Tree-Level-Order-Traversal.cpp)| _O(n)_ | _O(n)_ | Medium | Binary Tree, map | |
+| 2415 | [Reverse Odd Levels of Binary Tree](https://leetcode.com/problems/reverse-odd-levels-of-binary-tree) | [Java](./Java/ReverseOddLevelsOfBinaryTree.java) | _O(n)_ | _O(n)_ | Medium | Binary Tree
 
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