create 129.Sum-Root-To-Leaf-Numbers.java

Author: jdiaz286

java/0129-sum-root-to-leaf-numbers.java

@@ -0,0 +1,69 @@
+/**
+ * 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 {
+    /*
+        Time complexity: O(V) where V is the number of vertices
+        Space complexity: O(V) where V is the number of vertices
+    */
+
+    // keep track of the different root to node values as a string
+    List<String> rootToLeafs = new ArrayList<String>();
+
+    public int sumNumbers(TreeNode root) {
+        // track the sum that we want to add
+        int solution = 0;
+
+        String currentPath = "";
+
+        // execute a dfs to find the leaf nodes
+        findLeafNodes(root, currentPath);
+
+        // loop through all the paths, convert to int, add to solution
+        for(String curr:rootToLeafs){
+            // save the current string as an integer
+            int currentVal = Integer.parseInt(curr);
+
+            // add the current value to the solution
+            solution+=currentVal;
+        }
+
+        // return the solution
+        return solution;
+    }
+
+    // dfs method
+    public void findLeafNodes(TreeNode node, String currentPath){
+        // base case, if no node then return
+        if(node==null){
+            return;
+        }
+
+        // add the current node value to the currentPath string
+        currentPath+=Integer.toString(node.val);
+
+        // check the left most value
+        findLeafNodes(node.left, currentPath);
+
+        // check the right most value
+        findLeafNodes(node.right, currentPath);
+
+        // if we are at a non-null node, check if it is a leaf
+        if(node.left==null && node.right==null){
+            // add the currentPath to the arraylist
+            rootToLeafs.add(currentPath);
+        }
+    }
+}