1+ // --- Directions
2+ // Implement a Queue datastructure using two stacks.
3+ // *Do not* create an array inside of the 'Queue' class.
4+ // Queue should implement the methods 'add', 'remove', and 'peek'.
5+ // For a reminder on what each method does, look back
6+ // at the Queue exercise.
7+ 8+ // --- Examples
9+ // const q = new Queue();
10+ // q.add(1);
11+ // q.add(2);
12+ // q.peek(); should returns 1
13+ // q.remove(); should returns 1
14+ // q.remove(); should returns 2
15+ 16+ 17+ // Solution
18+ 19+ const Stack = require ( './stack' ) ;
20+ 21+ class Queue {
22+ constructor ( ) {
23+ this . first = new Stack ( ) ;
24+ this . second = new Stack ( ) ;
25+ }
26+ 27+ add ( record ) {
28+ this . first . push ( record ) ;
29+ }
30+ 31+ remove ( ) {
32+ while ( this . first . peek ( ) ) {
33+ this . second . push ( this . first . pop ( ) ) ;
34+ }
35+ 36+ const record = this . second . pop ( ) ;
37+ 38+ while ( this . second . peek ( ) ) {
39+ this . first . push ( this . second . pop ( ) ) ;
40+ }
41+ 42+ return record ;
43+ }
44+ 45+ 46+ peek ( ) {
47+ while ( this . first . peek ( ) ) {
48+ this . second . push ( this . first . pop ( ) ) ;
49+ }
50+ 51+ const record = this . second . peek ( ) ;
52+ 53+ while ( this . second . peek ( ) ) {
54+ this . first . push ( this . second . pop ( ) ) ;
55+ }
56+ }
57+ }
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