Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

 

思想：递归

1. public int height(TreeNode root) {
2. if(root==null) return 0;
3. if(root.left == null && root.right == null) return 1;
4. return Math.max(height(root.left),height(root.right))+1;
5. }
6. public boolean isBalanced(TreeNode root) {
7. if(root==null) return true;
8. if(root.left == null && root.right == null) return true;
9. if(isBalanced(root.right) == false || isBalanced(root.left) == false) {
10. return false;
11. }
12. if(Math.abs(height(root.left) - height(root.right))<=1) {
13. return true;
14. } else {
15. return false;
16. }
18. }

改进：仅遍历一次节点

1. bool isBalanced(TreeNode *root,int &height) {
3. if(root==NULL) {
4. height = 0;
5. return true;
6. }
7. int left = 0;
8. int lflag = isBalanced(root->left,left);
9. int right = 0;
10. int rflag = isBalanced(root->right,right);
11. if(lflag&&rflag) {
12. if(abs(left-right)<=1) {
13. height = max(left,right) + 1;
14. return true;
15. }
16. return false;
17. }
18. return false;
19. }
20. bool isBalanced(TreeNode *root) {
21. int height=0;
22. return isBalanced(root,height);
23. }