[24 May, 2020] add cpp solution2

Add solution with interpolation search

Iterative, time : ~O(n log logn), space : O(n)

Author: kerms

May-LeetCoding-Challenge/24-Construct-Binary-Search-Tree-From-Preorder-Traversal/Construct-Binary-Search-Tree-From-Preorder-Traversal.cpp

@@ -13,4 +13,47 @@ class Solution {
     TreeNode* bstFromPreorder(vector<int>& preorder) {
         return construct(0, preorder.size() - 1, preorder);
     }
-};
+};
+
+class Solution2 {
+public:
+    /* iterative, time : ~O(n log logn), space : O(n) */
+    TreeNode* bstFromPreorder(vector<int>& preorder) {
+        TreeNode **v = new TreeNode*[preorder.size()];
+        int curr_val, root_val = preorder[0];
+        int pos = 0;
+        TreeNode *root = new TreeNode(root_val);
+        TreeNode *node = root;
+        v[0] = root;
+        
+        for (int i = 1; i < preorder.size() ; ++i) {
+            curr_val = preorder[i];
+            if (preorder[i-1] > curr_val) {
+                node->left = new TreeNode(curr_val);
+                node = node->left;
+                v[++pos] = node;
+            } else { /* find the target father node */
+                if (curr_val > root_val) {
+                    pos = 0;
+                    root_val = curr_val;
+                } else {
+                    /* interpolation search, do more time if data is large */
+                    pos = ((curr_val - root_val) * (pos)) / (v[pos]->val - root_val);
+                    pos = max(0, pos);
+                    
+                    /* target is near pos */
+                    if (v[pos]->val > curr_val) {
+                        while (v[++pos]->val > curr_val);
+                    } else {
+                        while (curr_val > v[--pos]->val);
+                        ++pos;
+                    }
+                }
+                node = new TreeNode(curr_val);
+                v[pos]->right = node;
+                v[pos] = node;
+            }
+        }
+        return root;
+    }
+};