Create Convert Sorted List to Binary Search Tree.cpp

Author: daizhenyang

Convert Sorted List to Binary Search Tree.cpp

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+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+/**
+ * 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 *buildBalance(int len)
+    {
+        if (!len)return NULL;
+        int r=len/2;int l=r;
+        if (len%2==0)l--;
+        TreeNode *p=new TreeNode(0);
+        p->left=buildBalance(l);
+        p->right=buildBalance(r);
+        return p;
+    }
+    void inorder(TreeNode *p,ListNode * &head)
+    {
+        if (!p)return;
+        inorder(p->left,head);
+        p->val=head->val;
+        head=head->next;
+        inorder(p->right,head);
+    }
+    TreeNode *sortedListToBST(ListNode * head) {
+        // Start typing your C/C++ solution below
+        // DO NOT write int main() function
+        ListNode *ptr=head;
+        int len=0;
+        while (ptr)
+        {
+            len++;
+            ptr=ptr->next;
+        }
+        TreeNode *p=buildBalance(len);
+        inorder(p,head);
+        return p;
+    }
+};