Trees-3 Assignment Completed

Symmetric_tree.java

@@ -0,0 +1,64 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+ // Time Complexity = O(n)
+ // Space Complexity = O(n)
+ // using level order traversal - 
+ /*
+class Solution {
+    public boolean isSymmetric(TreeNode root) {
+        if(root==null) return true;
+        Queue<TreeNode> q = new LinkedList<>();
+        q.add(root.left);
+        q.add(root.right);
+        while(!q.isEmpty()){
+            TreeNode left = q.poll();
+            TreeNode right = q.poll();
+            if(left==null && right==null) continue;
+            if(left==null || right== null) return false;
+            if(left.val!=right.val) return false;
+            q.add(left.left);
+            q.add(right.right);
+            q.add(left.right);
+            q.add(right.left);
+        }
+        return true;
+    }
+}
+*/
+ // Time Complexity = O(n)
+ // Space Complexity = O(h)
+ // using recursion - 
+class Solution {
+    boolean flag;
+    public boolean isSymmetric(TreeNode root) {
+        if(root == null) return true;
+        this.flag = true;
+        helper(root.left, root.right);
+        return flag;
+    }
+    private void helper(TreeNode left, TreeNode right){
+        if(left==null && right==null) return;
+        if(left==null || right== null){
+            flag = false;
+            return;
+        } 
+        if(left.val!=right.val){
+            flag = false;
+        }
+        if(flag) helper(left.left,right.right);
+        if(flag) helper(left.right,right.left);
+    }
+}

path_sum_2.java

@@ -0,0 +1,39 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    List<List<Integer>> result;
+    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
+        this.result = new ArrayList<>();
+        helper(root,targetSum,0,new ArrayList<>());
+        return result;
+    }
+    private void helper(TreeNode root,int targetSum, int sum, List<Integer> path){
+        if(root==null) return ;
+
+        sum+=root.val;
+        path.add(root.val);
+        if(root.left==null && root.right==null){
+            if(sum==targetSum){
+                result.add(new ArrayList<>(path));
+            }
+        }
+        helper(root.left,targetSum,sum,path);
+        helper(root.right,targetSum,sum,path);
+
+        //backtrack
+        path.remove(path.size()-1);
+    }
+}