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Author: a93a

kotlin/0101-symmetric-tree.kt

@@ -0,0 +1,53 @@
+/*
+* Recursive solution
+*/
+class Solution {
+    fun isSymmetric(root: TreeNode?): Boolean {
+
+        fun dfs(left: TreeNode?, right: TreeNode?): Boolean {
+            if(left == null && right == null)
+                return true
+            if(left == null || right == null)
+                return false
+
+            return left.value == right.value &&
+                dfs(left.left, right.right) &&
+                dfs(left.right, right.left)
+        }
+
+        return dfs(root!!.left, root!!.right)
+    }
+
+    val TreeNode.value get()= this.`val`
+}
+
+/*
+* Iterative solution
+*/
+class Solution {
+    fun isSymmetric(root: TreeNode?): Boolean {
+       val q = LinkedList<TreeNode?>()
+       q.addFirst(root!!.left)
+       q.addFirst(root!!.right)
+
+        while(q.isNotEmpty()) {
+            val left = q.removeFirst()
+            val right = q.removeFirst()
+
+            if(left == null && right == null)
+                continue
+
+            if(left == null || right == null || left.value != right.value)
+                return false
+            
+            q.addFirst(left.left)
+            q.addFirst(right.right)
+            q.addFirst(left.right)
+            q.addFirst(right.left)
+        }
+
+        return true
+    }   
+
+    val TreeNode.value get()= this.`val`
+}