Convert Sorted Array to Binary Search Tree.

ConvertSortedArraytoBinarySearchTree.h

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+/*
+ Author:     Annie Kim, anniekim.pku@gmail.com
+ Date:       Apr 9, 2013
+ Problem:    Convert Sorted Array to Binary Search Tree
+ Difficulty: Easy
+ Source:     http://leetcode.com/onlinejudge#question_108
+ Notes:
+ Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
+
+ Solution: Recursion.
+ */
+
+/**
+ * Definition for binary tree
+ * 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) {
+        return buildBST(num, 0, num.size() - 1);
+    }
+
+    TreeNode *buildBST(vector<int> &num, int start, int end)
+    {
+        if (start > end) return NULL;
+
+        int mid = (start + end) / 2;
+        TreeNode *root = new TreeNode(num[mid]);
+        root->left = buildBST(num, start, mid - 1);
+        root->right = buildBST(num, mid + 1, end);
+
+        return root;
+    }
+};