Tree sum-root-to-leaf-numbers java (#22)

Author: girishgr8

Java/sum-root-to-leaf-numbers.java

@@ -0,0 +1,47 @@
+/**
+ * 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;
+ *     }
+ * }
+ * 
+ *  Runtime: 0 ms
+    Memory Usage: 39.2 MB
+ */
+
+class Solution {
+    int sum = 0;
+
+    public int sumNumbers(TreeNode root) {
+        traverse(root, 0);
+        return sum;
+    }
+
+    public void traverse(TreeNode root, int n) {
+        // if the node is null, return from the function (specially to handle if root of
+        // tree is null)
+        if (root == null)
+            return;
+        // shift the previous units place digit to ten's place by multiplying it by 10
+        // and add the current value of node
+        n = n * 10 + root.val;
+        // if the node does not have a left or right children is null,
+        // the current node is leaf node, so add the value to sum and return
+        if (root.left == null && root.right == null) {
+            sum += n;
+            return;
+        }
+        // recurse for left subtree
+        traverse(root.left, n);
+        // recurse for right subtree
+        traverse(root.right, n);
+    }
+}