trees-1

SumRoot.java

@@ -0,0 +1,19 @@
+import java.util.*;
+
+public class SumRoot {
+    int sum;
+    public int sumRoot(TreeNode root) {
+        helper(root, 0);
+        return sum;        
+    }
+    private void helper(TreeNode root, int currSum) {
+        if (root==null) return;
+
+        currSum = currSum * 10 + root.val;
+        if (root.right == null && root.left==null) {
+            sum += currSum;
+        }
+        helper(root.left, currSum);
+        helper(root.right, currSum);
+    }
+}

SumRootRec.java

@@ -0,0 +1,22 @@
+public class SumRootRec {
+    int sum;
+
+    public int sumNumbers(TreeNode root) {
+        return helper(root, 0);
+    }
+
+    public int helper(TreeNode root, int num) {
+        helper(root, 0);
+        return sum;        
+    }
+    private void helper(TreeNode root, int currSum) {
+        if (root==null) return;
+
+        currSum = currSum * 10 + root.val;
+        if (root.right == null && root.left==null) {
+            sum += currSum;
+        }
+        helper(root.left, currSum);
+        helper(root.right, currSum);
+    }
+}

ValidateBST.java

@@ -0,0 +1,23 @@
+import java.util.*;
+
+class ValidateBST {
+    boolean flag;
+    public boolean isValidBST(TreeNode root) {
+        this.flag = true;
+        helper(root, null, null);
+        return flag;
+    }
+    private void helper(TreeNode root, Integer min, Integer max) {
+        if (root==null) return;
+
+        helper(root.left, min, root.val);
+        if (min != null && root.val <= min) {
+            flag = false;
+        }
+        if (max != null && root.val >= max){
+            flag = false;
+        }
+        helper(root.right, root.val, max);
+
+    }
+}

ValidateBSTRecursive.java

@@ -0,0 +1,21 @@
+
+class ValidateBSTRecursive {
+    boolean flag;
+    TreeNode prev;
+
+    public boolean validateBSTRecursive(TreeNode root) {
+        this.flag = true;
+        helper(root);
+        return flag;
+    }
+    private void helper(TreeNode root) {
+        if (root==null) return;
+        if (!flag) return;
+        helper(root.left);
+        if (prev != null && root.val <= prev.val){
+            flag = false;
+        }
+        prev = root;
+        helper(root.right);
+    }
+}