/
StackMin.java
77 lines (61 loc) · 2.34 KB
/
StackMin.java
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
import java.util.Stack;
/**
* How would you design a stack which, in addition to push and pop, has a function min which returns the minimum
* element? Push, pop, and min should all operate in O(1) time.
*/
public class StackMin {
private Stack<Integer> mainstack = new Stack<>();
private Stack<Integer> minstack = new Stack<>();
public StackMin() {
}
public void push(Integer item) {
mainstack.push(item);
if(minstack.isEmpty()){
minstack.push(item);
} else {
if(minstack.peek() >= item){
minstack.push(item);
}
}
}
public int pop() {
if(mainstack.isEmpty()){
return -1;
} else {
if(mainstack.peek() == minstack.peek()){
minstack.pop();
}
return mainstack.pop();
}
}
public int min() {
if(minstack.isEmpty()){
return -1;
}
return minstack.peek();
}
public static void main(String[] args) {
StackMin sm = new StackMin();
sm.push(6);
System.out.println("Min after pushing 6 = " + sm.min());
sm.push(7);
System.out.println("Min after pushing 2 = " + sm.min());
sm.push(3);
System.out.println("Min after pushing 3 = " + sm.min());
sm.push(4);
System.out.println("Min after pushing 4 = " + sm.min());
sm.push(5);
System.out.println("Min after pushing 5 = " + sm.min());
sm.push(2);
System.out.println("Min after pushing 2 = " + sm.min());
System.out.println("\n Now popping....!");
System.out.println("Min after popping " + sm.pop() + " = " + sm.min());
System.out.println("Min after popping " + sm.pop() + " = " + sm.min());
System.out.println("Min after popping " + sm.pop() + " = " + sm.min());
System.out.println("Min after popping " + sm.pop() + " = " + sm.min());
System.out.println("Min after popping " + sm.pop() + " = " + sm.min());
System.out.println("Min after popping " + sm.pop() + " = " + sm.min());
System.out.println("Min after popping " + sm.pop() + " = " + sm.min());
System.out.println("Min after popping " + sm.pop() + " = " + sm.min());
}
}