forked from shuboc/LeetCode-2
-
Notifications
You must be signed in to change notification settings - Fork 0
/
min-stack.py
83 lines (72 loc) · 2 KB
/
min-stack.py
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
# Time: O(n)
# Space: O(1)
#
# Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
#
# push(x) -- Push element x onto stack.
# pop() -- Removes the element on top of the stack.
# top() -- Get the top element.
# getMin() -- Retrieve the minimum element in the stack.
#
class MinStack:
def __init__(self):
self.min = None
self.stack = []
# @param x, an integer
# @return an integer
def push(self, x):
if not self.stack:
self.stack.append(0)
self.min = x
else:
self.stack.append(x - self.min)
if x < self.min:
self.min = x
# @return nothing
def pop(self):
x = self.stack.pop()
if x < 0:
self.min = self.min - x
# @return an integer
def top(self):
x = self.stack[-1]
if x > 0:
return x + self.min
else:
return self.min
# @return an integer
def getMin(self):
return self.min
# Time: O(n)
# Space: O(n)
class MinStack2:
def __init__(self):
self.stack, self.minStack = [], []
# @param x, an integer
# @return an integer
def push(self, x):
self.stack.append(x)
if len(self.minStack):
if x < self.minStack[-1][0]:
self.minStack.append([x, 1])
elif x == self.minStack[-1][0]:
self.minStack[-1][1] += 1
else:
self.minStack.append([x, 1])
# @return nothing
def pop(self):
x = self.stack.pop()
if x == self.minStack[-1][0]:
self.minStack[-1][1] -= 1
if self.minStack[-1][1] == 0:
self.minStack.pop()
# @return an integer
def top(self):
return self.stack[-1]
# @return an integer
def getMin(self):
return self.minStack[-1][0]
if __name__ == "__main__":
stack = MinStack()
stack.push(-1)
print [stack.top(), stack.getMin()]