tasks a-s

Task/Queue-Definition/Go/queue-definition.go

@@ -0,0 +1,55 @@
+package queue
+
+// int queue
+// the zero object is a valid queue ready to be used.
+// items are pushed at tail, popped at head.
+// tail = -1 means queue is full
+type Queue struct {
+    b []string
+    head, tail int
+}
+
+func (q *Queue) Push(x string) {
+    switch {
+    // buffer full. reallocate.
+    case q.tail < 0:
+        next := len(q.b)
+        bigger := make([]string, 2*next)
+        copy(bigger[copy(bigger, q.b[q.head:]):], q.b[:q.head])
+        bigger[next] = x
+        q.b, q.head, q.tail = bigger, 0, next+1
+    // zero object. make initial allocation.
+    case len(q.b) == 0:
+        q.b, q.head, q.tail = make([]string, 4), 0 ,1
+        q.b[0] = x
+    // normal case
+    default:
+        q.b[q.tail] = x
+        q.tail++
+        if q.tail == len(q.b) {
+            q.tail = 0
+        }
+        if q.tail == q.head {
+            q.tail = -1
+        }
+    }
+}
+
+func (q *Queue) Pop() (string, bool) {
+    if q.head == q.tail {
+        return "", false
+    }
+    r := q.b[q.head]
+    if q.tail == -1 {
+        q.tail = q.head
+    }
+    q.head++
+    if q.head == len(q.b) {
+        q.head = 0
+    }
+    return r, true
+}
+
+func (q *Queue) Empty() bool {
+    return q.head == q.tail
+}