java-57-Queue && Implement a stack with two queues with two stacks

Transferred from: http://bylijinnan.iteye.com/blog/1450125

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Java code

2. Import java.util.ArrayList;
4. Import java.util.List;
6. Import Java.util.Stack;
10. /*  
12. * Q 57 with two stacks to implement a queue
14. */
18. Public class Queueimplementbytwostacks {
22. private stack<integer> Stack1;
24. private stack<integer> Stack2;
28. Queueimplementbytwostacks () {
30. stack1=new stack<integer> ();
32. stack2=new stack<integer> ();
34. }
38. Public Integer Poll () {
40. Integer re=null;
42. if (!stack2.empty ()) {
44. Re=stack2.pop ();
46. }else{
48. While (!stack1.empty ()) {//move to Stack2 to make Stack1 has only oneelement.   Then pops this element.
50. Re=stack1.pop ();
52. Stack2.push (re);
54. }
56. if (!stack2.empty ()) {
58. Re=stack2.pop ();
60. }
62. }
64. return re;
66. }
68. Public Integer Offer (int o) {
70. Stack1.push (o);
72. return o;
74. }
78. public static void Main (string[] args) {
80. Queueimplementbytwostacks queue=New Queueimplementbytwostacks ();
82. list<integer> re=New arraylist<integer> ();
84. Queue.offer (1);
86. Queue.offer (2);
88. Queue.offer (3);
90. Re.add (Queue.poll ());
92. Queue.offer (4);
94. Re.add (Queue.poll ());
96. Queue.offer (5);
98. Re.add (Queue.poll ());
100. Re.add (Queue.poll ());
102. Re.add (Queue.poll ());
104. System.out.println (Re.tostring ());
106. }
110. }

Import Java.util.arraylist;import java.util.list;import java.util.stack;/* * Q 57 Implement Queue */public class with two stacks queueimplementbytwostacks {private stack<integer> stack1;private stack<integer> Stack2; Queueimplementbytwostacks () {stack1=new stack<integer> (); stack2=new stack<integer> ();} Public Integer Poll () {Integer re=null;if (!stack2.empty ()) {Re=stack2.pop ();} Else{while (!stack1.empty ()) {//move to Stack2 and make Stack1 has only one element. Then pops this element.re=stack1.pop (); Stack2.push (re);} if (!stack2.empty ()) {Re=stack2.pop ();}} return re;} Public Integer offer (int o) {stack1.push (o); return o;} public static void Main (string[] args) {queueimplementbytwostacks queue=new queueimplementbytwostacks (); List<integer> re=new arraylist<integer> (); Queue.offer (1); Queue.offer (2); Queue.offer (3); Re.add ( Queue.poll ()); Queue.offer (4); Re.add (Queue.poll ()); Queue.offer (5); Re.add (Queue.poll ()); Re.add (Queue.poll ()); Re.add (Queue.poll ()); System.out.println (Re.tostring ());}}

Java code

2. Import java.util.LinkedList;
6. /*  
8. * Q 57 Implementation of a stack with two queues
10. */
12. Public class Stackimplementbytwoqueues {
16. //use ' queue1 ' and ' queue2 ' as a queue.   That means only use the method ' AddLast ' and ' Removefirst '.
18. private linkedlist<integer> queue1;
20. private linkedlist<integer> queue2;
24. Stackimplementbytwoqueues () {
26. queue1=new linkedlist<integer> ();
28. queue2=new linkedlist<integer> ();
30. }
34. Public Integer Pop () {
36. Integer re=null;
38. if (queue1.size () = =0&&queue2.size () = =0) {
40. return null;
42. }
44. if (queue2.size () = =0) {
46. While (Queue1.size () >0) {
48. Re=queue1.removefirst ();
50. if (queue1.size ()! =0) {//do not add the last element of Queue1 to Queue2
52. Queue2.addlast (re);
54. }
56. }
58. }Else if (queue1.size () = =0) {
60. While (Queue2.size () >0) {
62. Re=queue2.removefirst ();
64. if (queue2.size ()! =0) {//do not add the last element of Queue2 to Queue1
66. Queue1.addlast (re);
68. }
70. }
72. }
74. return re;
76. }
78. Public integer push (integer o) {
80. if (queue1.size () = =0&&queue2.size () = =0) {
82. Queue1.addlast (o); //queue2.addlast (o); is also OK
84. }
86. if (queue1.size ()! =0) {
88. Queue1.addlast (o);
90. }Else if (queue2.size ()! =0) {
92. Queue2.addlast (o);
94. }
96. return o;
98. }
102. public static void Main (string[] args) {
104. Stackimplementbytwoqueues stack=New Stackimplementbytwoqueues ();
106. int tmp=0;
108. Stack.push (1);
110. Stack.push (2);
112. Stack.push (3);
114. Tmp=stack.pop ();
116. SYSTEM.OUT.PRINTLN (TMP); //3
118. Stack.push (4);
120. Tmp=stack.pop ();
122. SYSTEM.OUT.PRINTLN (TMP); //4
124. Tmp=stack.pop ();
126. SYSTEM.OUT.PRINTLN (TMP); //2
128. Stack.push (5);
130. Stack.push (6);
132. Tmp=stack.pop ();
134. SYSTEM.OUT.PRINTLN (TMP); //6
136. Tmp=stack.pop ();
138. SYSTEM.OUT.PRINTLN (TMP); //5
140. Tmp=stack.pop ();
142. SYSTEM.OUT.PRINTLN (TMP); //1
144. }
146. }

java-57-Queue && Implement a stack with two queues with two stacks