fix(rpn): optimize Swap from O(n) to O(1) (task dj)

Replace stack.Values() with direct Pop() calls in Swap().
Previously created a full stack copy just to read the top two values.
Behavior is unchanged — ensureStackLength guard guarantees pops succeed.

1 files changed, 2 insertions, 14 deletions

diff --git a/internal/rpn/operations_stack.go b/internal/rpn/operations_stack.go
index c028ab7..99eaa8b 100644
--- a/internal/rpn/operations_stack.go
+++ b/internal/rpn/operations_stack.go
@@ -4,7 +4,6 @@
 package rpn
 
 import (
-	"fmt"
 	"strings"
 )
 
@@ -26,20 +25,9 @@ func (o *Operations) Swap(stack *Stack) error {
 		return err
 	}
 
-	// Get the values without popping
-	vals := stack.Values()
-	top := vals[len(vals)-1]
-	second := vals[len(vals)-2]
-
-	// Pop both values
-	if _, err := stack.Pop(); err != nil {
-		return buildError("swap", fmt.Errorf("failed to pop top value: %w", err))
-	}
-	if _, err := stack.Pop(); err != nil {
-		return buildError("swap", fmt.Errorf("failed to pop second value: %w", err))
-	}
+	top, _ := stack.Pop()
+	second, _ := stack.Pop()
 
-	// Push in swapped order
 	stack.Push(top)
 	stack.Push(second)