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SymmetricTree.java
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67 lines (60 loc) · 1.98 KB
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/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class RecursiveSolution {
public boolean isSymmetricRecursive(TreeNode root) {
if (root == null) {
return true;
}
return this.check(root.left, root.right);
}
public boolean check(TreeNode left, TreeNode right) {
if (left == null && right == null) {
return true;
}
if ((left == null && right != null) || (left != null && right == null) || (left.val != right.val)) {
return false;
}
return this.check(left.left, right.right) && this.check(left.right, right.left);
}
}
public class IterativeSolution {
public boolean isSymmetric(TreeNode root) {
if (root == null) {
return true;
}
Stack<TreeNode> left = new Stack<TreeNode>();
Stack<TreeNode> right = new Stack<TreeNode>();
TreeNode leftRoot = root.left;
TreeNode rightRoot = root.right;
while (left.isEmpty() == false || leftRoot != null) {
if (leftRoot != null) {
if (rightRoot == null) {
return false;
}
left.push(leftRoot);
right.push(rightRoot);
leftRoot = leftRoot.left;
rightRoot = rightRoot.right;
} else {
if (right.isEmpty() || rightRoot != null) {
return false;
}
TreeNode currLeft = left.pop();
TreeNode currRight = right.pop();
if (currLeft.val != currRight.val) {
return false;
}
leftRoot = currLeft.right;
rightRoot = currRight.left;
}
}
return right.isEmpty() && rightRoot == null;
}
}