108.Convert Sorted Array to Binary Search Tree(Array; Divide-and-Conquer, dfs)

標籤：

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

思路：使用二分法，將list的中間節點作為根節點，然後分別處理list左半邊及右半邊，以此遞迴。

struct TreeNode {   int val;   TreeNode *left;   TreeNode *right;   TreeNode(int x) : val(x), left(NULL), right(NULL) {}};class Solution {public:    TreeNode *sortedArrayToBST(vector<int> &num) {        if(num.empty()) return NULL;        TreeNode* root = new TreeNode(0);        dfs(num,0,num.size()-1,root);                  return root;    }    void dfs(vector<int> &num,int start, int end,TreeNode* treeNode)    {        int size = end-start+1;        if(size == 1)        {            treeNode->val = num[start];            return;        }        int mid = size/2 + start;        treeNode->val = num[mid];              treeNode->left = new TreeNode(0);        dfs(num,start,mid-1,treeNode->left);        if(mid+1<=end)        {            treeNode->right = new TreeNode(0);            dfs(num,mid+1,end,treeNode->right);        }      }};

 

108.Convert Sorted Array to Binary Search Tree(Array; Divide-and-Conquer, dfs)