-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathStack.java
More file actions
127 lines (116 loc) · 2.77 KB
/
Copy pathStack.java
File metadata and controls
127 lines (116 loc) · 2.77 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
package jiuzhang.java.elementary;
public class Stack {
//*Note: good way, it is hard to keep track of previous node, why not operate at the beginning of the list
// beginning of list is the top of the stack, do push as insert element at the head of list
// And also use the dummy to make preInsersion of the head to postInsertion of the dummy
class ListNode {
private int val;
public ListNode next;
ListNode(int val){
this.val = val;
}
}
ListNode dummy;
Stack() {
dummy = new ListNode(-1); //dummy always point to the head of the list
}
public void push(int x) {
// write your code here
ListNode node = new ListNode(x);
node.next = dummy.next;
dummy.next = node;
}
/*
* @return: nothing
*/
public void pop() {
// write your code here
dummy.next = dummy.next.next;
}
/*
* @return: An integer
*/
public int top() {
// write your code here
if (isEmpty()) {
return -1;
}
return dummy.next.val;
}
/*
* @return: True if the stack is empty
*/
public boolean isEmpty() {
// write your code here
return dummy.next == null;
}
//
// //bad way
// /*
// * @param x: An integer
// * @return: nothing
// */
// class ListNode {
// private int val;
// public ListNode next;
// ListNode(int val){
// this.val = val;
// }
// }
//
// private ListNode dummy, tail;
//
// private int size;
//
// Stack() {
// size = 0;
// dummy = new ListNode(0);
// tail = null;
// }
//
//
// public void push(int x) {
// // write your code here
// if (this.size == 0) {
// dummy.next = new ListNode(x);
// tail = dummy.next;
// } else {
// tail.next = new ListNode(x);
// tail = tail.next;
// }
// size++;
// }
//
// /*
// * @return: nothing
// */
// public void pop() {
// // write your code here
// ListNode preTail = dummy;
// while (preTail.next.next != null) { //*Note: this take to much time
// preTail = preTail.next;
// }
// tail = preTail;
// preTail.next = null;
// size--;
// }
//
// /*
// * @return: An integer
// */
// public int top() {
// // write your code here
// if (this.isEmpty()) {
// return -1;
// }
// return tail.val;
// }
//
// /*
// * @return: True if the stack is empty
// */
// public boolean isEmpty() {
// // write your code here
// return size == 0;
// }
}