Merge pull request #14 from Morbo-ui/main

neetcode-gh · web-flow · commit bd6cf3c29bd2 · 2022-04-03T21:52:27.000-07:00
Added Java 98-Validate-Binary-Search-Tree and Java 21-Merge-Two-Sorted-Lists
diff --git a/java/21-Merge-Two-Sorted-Lists.java b/java/21-Merge-Two-Sorted-Lists.java
@@ -0,0 +1,30 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
+        final ListNode root = new ListNode();
+        ListNode prev = root;
+        while (list1 != null && list2 != null) {
+            if(list1.val < list2.val) {
+
+
+                prev.next = list1;
+                list1 = list1.next;
+            } else {
+                prev.next = list2;
+                list2 = list2.next;
+            }
+            prev = prev.next;
+        }
+        prev.next = list1 != null ? list1 : list2;
+        return root.next;
+    }
+}
diff --git a/java/98-Validate-Binary-Search-Tree.java b/java/98-Validate-Binary-Search-Tree.java
@@ -0,0 +1,33 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode() {}
+ * TreeNode(int val) { this.val = val; }
+ * TreeNode(int val, TreeNode left, TreeNode right) {
+ * this.val = val;
+ * this.left = left;
+ * this.right = right;
+ * }
+ * }
+ */
+class Solution {
+    public boolean isValidBST(TreeNode root) {
+        if (root == null) return true;
+        return dfs(root, null, null);
+    }
+
+    private boolean dfs(TreeNode root, Integer min, Integer max) {
+        if (root == null) return true;
+
+        if ((min != null && root.val <= min) || max != null && root.val >= max) {
+            return false;
+        }
+
+        return dfs(root.left, min, root.val) && dfs(root.right, root.val, max);
+
+    }
+}
+
