Improve day 5

day05/common/crane.go

@@ -16,11 +16,15 @@ func (stack *Stack) Push(crate byte) {
   *stack = append(*stack, crate)
 }
 
-func (stack *Stack) Pop() byte {
+func (stack *Stack) Pop() (byte, bool) {
   last := len(*stack) - 1
-  top := (*stack)[last]
-  *stack = (*stack)[:last]
-  return top
+  if last >= 0 {
+    top := (*stack)[last]
+    *stack = (*stack)[:last]
+    return top, true
+  } else {
+    return 0, false
+  }
 }
 
 func (stack *Stack) Peek() byte {