diff --git a/sum-of-left-leaves/sol.go b/sum-of-left-leaves/sol.go
new file mode 100644
index 0000000..7246a30
--- /dev/null
+++ b/sum-of-left-leaves/sol.go
@@ -0,0 +1,23 @@
+package main
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+// Time: O(n)
+// Space: O(1)
+func sumOfLeftLeaves(root *TreeNode) int {
+	return soll(root, false)
+}
+
+func soll(root *TreeNode, include bool) int {
+	if root == nil {
+		return 0
+	}
+	if root.Left == nil && root.Right == nil && include {
+		return root.Val
+	}
+	return soll(root.Left, true) + soll(root.Right, false)
+}