day24

Author: khushi3004

Day24-ConstructBinarySearchTreefromPreorderTraversal.java

@@ -0,0 +1,35 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public TreeNode bstFromPreorder(int[] preorder) {
+        return construct(preorder,0,preorder.length-1);
+    }
+    
+    public TreeNode construct(int[] pre,int start,int end){
+        if(start>end) return null;
+        
+        TreeNode root=new TreeNode(pre[start]);
+        
+        int val=-1;
+        for(int i=start+1;i<=end;i++){
+            if(pre[i]>pre[start]){
+                val=i;
+                break;
+            }
+        }
+        
+        if(val==-1) 
+            val=end+1;
+        root.left=construct(pre,start+1,val-1);
+        root.right=construct(pre,val,end);
+        
+        return root;
+    }
+}