Create Ostrichcrab.md

Ostrichcrab · web-flow · commit c9e88e36379a · 2018-12-08T12:31:54.000+08:00
diff --git a/2018.12.08-leetcode105/Ostrichcrab.md b/2018.12.08-leetcode105/Ostrichcrab.md
@@ -0,0 +1,25 @@
+```
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public TreeNode buildTreeHelper(int[] inorder, int is, int ie, int[] preorder, int ps){
+        if(is>ie || ps>=preorder.length) return null;
+        TreeNode root = new TreeNode(preorder[ps]);
+        int rootAtIn = is;
+        while(inorder[rootAtIn] != root.val) rootAtIn++;
+        root.left = buildTreeHelper(inorder,is,rootAtIn-1,preorder,ps+1);
+        root.right = buildTreeHelper(inorder,rootAtIn+1,ie,preorder,ps+rootAtIn-is+1);
+        return root;
+    }
+    public TreeNode buildTree(int[] preorder, int[] inorder) {
+        return buildTreeHelper(inorder,0,inorder.length-1,preorder,0);
+    }
+}
+```
