diff --git a/solution/42/main.go b/solution/42/main.go
new file mode 100644
index 0000000..ec76c1c
--- /dev/null
+++ b/solution/42/main.go
@@ -0,0 +1,24 @@
+package main
+
+func trap(height []int) int {
+    n := len(height)
+    res := 0
+    var st []int
+
+    for r := 0; r < n; r++ {
+        for len(st) > 0 && height[st[len(st) - 1]] <= height[r] {
+            m := st[len(st) - 1] 
+            st = st[:len(st) - 1]
+
+            if len(st) > 0 {
+                l := st[len(st) - 1]
+                d := min(height[l], height[r])
+                k := r - 1 - (l + 1) + 1
+                res += k * (d - height[m])
+            }
+        }
+        st = append(st, r)
+    }
+
+    return res
+}