Create 1008-construct-binary-search-tree-from-preorder-traversal.js

Author: everthis

1008-construct-binary-search-tree-from-preorder-traversal.js

@@ -0,0 +1,51 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {number[]} preorder
+ * @return {TreeNode}
+ */
+const bstFromPreorder = function(preorder) {
+  let preIndex = { index: 0 };
+  return constructTreeUtil(
+    preorder,
+    preIndex,
+    preorder[0],
+    Number.MIN_SAFE_INTEGER,
+    Number.MAX_SAFE_INTEGER,
+    preorder.length
+  );
+  function constructTreeUtil(pre, preIndex, key, min, max, size) {
+    if (preIndex.index >= size) {
+      return null;
+    }
+    let root = null;
+    if (key > min && key < max) {
+      root = new TreeNode(key);
+      preIndex.index = preIndex.index + 1;
+      if (preIndex.index < size) {
+        root.left = constructTreeUtil(
+          pre,
+          preIndex,
+          pre[preIndex.index],
+          min,
+          key,
+          size
+        );
+        root.right = constructTreeUtil(
+          pre,
+          preIndex,
+          pre[preIndex.index],
+          key,
+          max,
+          size
+        );
+      }
+    }
+    return root;
+  }
+};