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| 1 | +package Blind75; |
| 2 | + |
| 3 | +import java.util.Stack; |
| 4 | + |
| 5 | +class TreeNode { |
| 6 | + int val; |
| 7 | + TreeNode left; |
| 8 | + TreeNode right; |
| 9 | + TreeNode() {} |
| 10 | + TreeNode(int val) { this.val = val; } |
| 11 | + TreeNode(int val, TreeNode left, TreeNode right) { |
| 12 | + this.val = val; |
| 13 | + this.left = left; |
| 14 | + this.right = right; |
| 15 | + } |
| 16 | +} |
| 17 | +public class Lt101 { |
| 18 | + public static void main(String[] args) { |
| 19 | + |
| 20 | + } |
| 21 | + |
| 22 | + //Recursive solution fastest |
| 23 | + public boolean isSymmetric(TreeNode root) { |
| 24 | + |
| 25 | + if(root == null){ return false;} |
| 26 | + |
| 27 | + return checkSymmetric(root.left, root.right); |
| 28 | + } |
| 29 | + |
| 30 | + public boolean checkSymmetric(TreeNode leftParent, TreeNode rightParent){ |
| 31 | + |
| 32 | + if(leftParent == null && rightParent == null){return true;} |
| 33 | + if(leftParent == null || rightParent == null){return false;} |
| 34 | + if(leftParent.val != rightParent.val){return false;} |
| 35 | + |
| 36 | + return checkSymmetric(leftParent.left, rightParent.right) && checkSymmetric(leftParent.right, rightParent.left); |
| 37 | + |
| 38 | + } |
| 39 | + //Iterative solution slower than recursion and with stack help |
| 40 | + public boolean isSymmetric2(TreeNode root) { |
| 41 | + if (root == null) return true; |
| 42 | + Stack<TreeNode> stack = new Stack<>(); |
| 43 | + stack.push(root.left); |
| 44 | + stack.push(root.right); |
| 45 | + while (!stack.empty()) { |
| 46 | + TreeNode n1 = stack.pop(), n2 = stack.pop(); |
| 47 | + if (n1 == null && n2 == null) continue; |
| 48 | + if (n1 == null || n2 == null || n1.val != n2.val) return false; |
| 49 | + stack.push(n1.left); |
| 50 | + stack.push(n2.right); |
| 51 | + stack.push(n1.right); |
| 52 | + stack.push(n2.left); |
| 53 | + } |
| 54 | + return true; |
| 55 | + } |
| 56 | +} |
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