[leetcode][155] Min Stack
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.
Example:
MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); --> Returns -3. minStack.pop(); minStack.top(); --> Returns 0. minStack.getMin(); --> Returns -2.
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class MinStack(object):
def __init__(self):
"""
initialize your data structure here.
"""
self.stack = []
self.min_val = None
self.min_idx = None
def push(self, x):
"""
:type x: int
:rtype: void
"""
if self.min_val is None:
self.min_val = x
self.min_idx = 0 # exclude repulicated values
self.stack.append(x)
elif x < self.min_val:
self.min_val = x
self.stack.append(x)
self.min_idx = len(self.stack) - 1
else:
self.stack.append(x)
def pop(self):
"""
:rtype: void
"""
# is poped value is min_val
if self.min_idx == len(self.stack) -1: # Probability is 1/n
new_stack = self.stack[:-1]
if new_stack: # O(n) some times
self.min_val = min(new_stack)
self.min_idx = new_stack.index(self.min_val)
else:
self.min_val = None
self.min_idx = None
self.stack.pop()
if len(self.stack) == 0:
self.min_val = None
self.min_idx = None
def top(self):
"""
:rtype: int
"""
return self.stack[-1]
def getMin(self):
"""
:rtype: int
"""
return self.min_val
# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(x)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()