Add path sum

Author: Gituser143

Easy/path-sum.md

@@ -0,0 +1,35 @@
+Code
+====
+
+```go
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func hasPathSum(root *TreeNode, sum int) bool {
+	if root == nil {
+		return false
+	}
+
+	if root.Val-sum == 0 {
+		if root.Right == nil && root.Left == nil {
+			return true
+		}
+	}
+
+	return hasPathSum(root.Right, sum-root.Val) || hasPathSum(root.Left, sum-root.Val)
+}
+```
+
+Solution in mind
+================
+
+-	If current node value - sum is equal to 0, AND the node is a leaf node, we have a valid path sum.
+
+-	If we ever encounter a nil node, we have reached the end of path and the path is not valid.
+
+-	We recursively call to see if either the right sub path or left sub path has a sum equal to sum - current node value.

README.md

@@ -23,6 +23,8 @@ Easy
 
 -	[merge-sorted-array](Easy/merge-sorted-array.md)
 
+-	[path-sum](Easy/path-sum.md)
+
 Medium
 ------