add Replace()

deque.go

@@ -216,6 +216,16 @@ func (q *Deque) Remove(i int) interface{} {
 	return elem
 }
 
+// Replace replaces the element at position i with the given element.  Accepts
+// only non-negative index values, and panics if index is out of range
+func (q *Deque) Replace(i int, elem interface{}) {
+	if i < 0 || i >= q.count {
+		panic("deque: Remove() called with index out of range")
+	}
+	// bitwise modulus
+	q.buf[(q.head+i)&(len(q.buf)-1)] = elem
+}
+
 // Clear removes all elements from the queue, but retains the current capacity.
 // The queue will not be resized smaller as long as items are only added.
 // Only when items are removed is the queue subject to getting resized smaller.

deque_test.go

@@ -395,6 +395,28 @@ func TestRemove(t *testing.T) {
 	}
 }
 
+func TestReplace(t *testing.T) {
+	var q Deque
+	q.PushBack("a")
+	q.PushBack("b")
+	q.PushBack("c")
+
+	q.Replace(0, "A")
+	if q.Front() != "A" {
+		t.Error("expected A at front")
+	}
+
+	q.Replace(q.Len()-1, "C")
+	if q.Back() != "C" {
+		t.Error("expected C at back")
+	}
+
+	q.Replace(1, "-")
+	if q.Peek(1) != "-" {
+		t.Error("expected - at position 1")
+	}
+}
+
 func TestPeekOutOfRangePanics(t *testing.T) {
 	var q Deque
 
@@ -498,6 +520,24 @@ func TestRemoveOutOfRangePanics(t *testing.T) {
 	})
 }
 
+func TestReplaceOutOfRangePanics(t *testing.T) {
+	var q Deque
+
+	assertPanics(t, "should panic when replacing in empty queue", func() {
+		q.Replace(0, "x")
+	})
+
+	q.PushBack("A")
+
+	assertPanics(t, "should panic when replacing at negative index", func() {
+		q.Replace(-1, "Z")
+	})
+
+	assertPanics(t, "should panic when replacing out of range", func() {
+		q.Replace(1, "Y")
+	})
+}
+
 func assertPanics(t *testing.T, name string, f func()) {
 	defer func() {
 		if r := recover(); r == nil {