For a binary tree T, we can define a flip operation as follows: choose any node, and swap the left and right child subtrees. A binary tree X is flip equivalent to a binary tree Y if and only if we can make X equal to Y after some number of flip operations. Write a function that determines whether two binary trees are flip equivalent. The trees are given by root nodes root1 and root2.
Example 1:
Input: root1 = [1,2,3,4,5,6,null,null,null,7,8], root2 = [1,3,2,null,6,4,5,null,null,null,null,8,7]
Output: true
Explanation: We flipped at nodes with values 1, 3, and 5.
Flipped Trees Diagram
Note:
- Each tree will have at most 100 nodes.
- Each value in each tree will be a unique integer in the range [0, 99].
Solution in C++
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: int ChildSum(TreeNode *node) { if (!node) return 0; int sum=0; if (node->left) sum += node->left->val; if (node->right) sum += node->right->val; return sum; } int ChildVal(TreeNode *node) { if (node) return node->val; return 0; } bool flipEquiv(TreeNode* root1, TreeNode* root2) { if (!root1 && !root2) return true; if (ChildVal(root1) != ChildVal(root2)) return false; if (ChildSum(root1)!=ChildSum(root2)) return false; if (root1->left) { if (root2->left && ChildVal(root1->left)==ChildVal(root2->left)) return flipEquiv(root1->left, root2->left) && flipEquiv(root1->right, root2->right); else return flipEquiv(root1->left, root2->right) && flipEquiv(root1->right, root2->left); } else if (root1->right) { if (root2->right && ChildVal(root1->right)==ChildVal(root2->right)) return flipEquiv(root1->right, root2->right) && flipEquiv(root1->left, root2->left); else return flipEquiv(root1->right, root2->left) && flipEquiv(root1->left, root2->right); } return true; } };
Solution in Java based on Recursion
class Solution(object): def flipEquiv(self, root1, root2): if root1 is root2: return True if not root1 or not root2 or root1.val != root2.val: return False return (self.flipEquiv(root1.left, root2.left) and self.flipEquiv(root1.right, root2.right) or self.flipEquiv(root1.left, root2.right) and self.flipEquiv(root1.right, root2.left))
Solution in Python based on Recursion
class Solution(object): def flipEquiv(self, root1, root2): if root1 is root2: return True if not root1 or not root2 or root1.val != root2.val: return False return (self.flipEquiv(root1.left, root2.left) and self.flipEquiv(root1.right, root2.right) or self.flipEquiv(root1.left, root2.right) and self.flipEquiv(root1.right, root2.left))
Solution in Java based on Canonical Traversal
class Solution { public boolean flipEquiv(TreeNode root1, TreeNode root2) { List<Integer> vals1 = new ArrayList(); List<Integer> vals2 = new ArrayList(); dfs(root1, vals1); dfs(root2, vals2); return vals1.equals(vals2); } public void dfs(TreeNode node, List<Integer> vals) { if (node != null) { vals.add(node.val); int L = node.left != null ? node.left.val : -1; int R = node.right != null ? node.right.val : -1; if (L < R) { dfs(node.left, vals); dfs(node.right, vals); } else { dfs(node.right, vals); dfs(node.left, vals); } vals.add(null); } } }
Solution in Python based on Canonical Traversal
class Solution: def flipEquiv(self, root1, root2): def dfs(node): if node: yield node.val L = node.left.val if node.left else -1 R = node.right.val if node.right else -1 if L < R: yield from dfs(node.left) yield from dfs(node.right) else: yield from dfs(node.right) yield from dfs(node.left) yield '#' return all(x == y for x, y in itertools.zip_longest( dfs(root1), dfs(root2)))