LeetCode-222. Count Complete Tree Nodes
阿新 • • 發佈:2018-12-09
Given a complete binary tree, count the number of nodes.
Note:
Definition of a complete binary tree from Wikipedia: In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
Example:
Input:
1
/ \
2 3
/ \ /
4 5 6
Output: 6
題解:原來直接返回1 + countNodes(root->left) + countNodes(root->right)會報超時,看別人分析,滿二叉樹可以單獨處理。
class Solution { public: int countNodes(TreeNode* root) { TreeNode *p = root, *q = root; if (!root){ return 0; } int l = 0, r = 0; while (p){ l++; p = p->left; } while (q){ r++; q = q->right; } if (r == l){ return pow(2, l) - 1; } return 1 + countNodes(root->left) + countNodes(root->right); } };