***Leetcode 894. All Possible Full Binary Trees
阿新 • • 發佈:2019-01-09
/** * 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: vector<TreeNode*> allPossibleFBT(int N) { mem.clear(); return dfs(N); } vector<TreeNode*> dfs(int n) { if (mem.find(n) != mem.end() ) return mem[n]; vector<TreeNode*> ret; if (n == 1) { ret.push_back(new TreeNode(0)); mem[n] = ret; return ret; } for (int i = 1; i < n; i+=2) { vector<TreeNode*> left = dfs(i); vector<TreeNode*> right = dfs(n-i-1); for (int j = 0; j < left.size(); j++) { for ( int k = 0; k < right.size(); k++ ) { TreeNode* root = new TreeNode(0); root->left = left[j]; root->right = right[k]; ret.push_back(root); } } } return ret; } private: map< int, vector<TreeNode*> > mem; };