Create 113_path_sum_II.md

Author: Joseph Luce

leetcode/medium/113_path_sum_II.md

@@ -0,0 +1,32 @@
+# 113. Path Sum II
+
+## Recursive Solution
+- Runtime: O(N)
+- Space: O(N)
+- N = Number of nodes in tree
+
+There are a few things that need to be added outside of a normal traversal of a binary tree.
+Outside of these things, everything else is a post order traversal.
+
+1. Keep track of the sum as we traverse.
+2. Have a result we can modify as we traverse.
+3. Keep track of what nodes we have already traversed for when we find a matching sum.
+
+```
+class Solution:
+    def pathSum(self, root: TreeNode, target: int) -> List[List[int]]:
+        def path_sum_helper(root, target, curr_sum, result, stack):
+            if root is None:
+                return
+            stack.append(root.val)
+            curr_sum += root.val
+            if root.left is None and root.right is None and target == curr_sum:
+                result.append([s for s in stack])
+            path_sum_helper(root.left, target, curr_sum, result, stack)
+            path_sum_helper(root.right, target, curr_sum, result, stack)
+            stack.pop()
+            
+        result = list()
+        path_sum_helper(root, target, 0, result, [])
+        return result
+```